diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 8f497af..25a3d1b 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -15,6 +15,7 @@ jobs:
   required:
     needs:
       - test
+      - coverage
       - lint
     runs-on: ubuntu-latest
     steps:
@@ -22,7 +23,7 @@ jobs:
   test:
     strategy:
       matrix:
-        go-version: [1.18.x, 1.19.x]
+        go-version: [1.19.x, 1.20.x]
     runs-on: ubuntu-latest
     steps:
       - name: Install Go
@@ -40,6 +41,22 @@ jobs:
         run: go build ./...
       - name: Test
         run: go test -bench . ./...
+  coverage:
+    needs:
+      - test
+    runs-on: ubuntu-latest
+    steps:
+      - name: Install Go
+        uses: actions/setup-go@c4a742cab115ed795e34d4513e2cf7d472deb55f # v3.3.1
+        with:
+          go-version: 1.20.x
+          check-latest: true
+      - name: Checkout code
+        uses: actions/checkout@93ea575cb5d8a053eaa0ac8fa3b40d7e05a33cc8 # v3.1.0
+        with:
+          persist-credentials: false
+      - name: Bootstrap
+        run: ./script/bootstrap
       - name: Coverage
         run: ./script/coverage
       - name: Upload Unit Test Coverage
@@ -60,7 +77,7 @@ jobs:
       - name: Install Go
         uses: actions/setup-go@c4a742cab115ed795e34d4513e2cf7d472deb55f # v3.3.1
         with:
-          go-version: 1.19.x
+          go-version: 1.20.x
           check-latest: true
       - name: Checkout code
         uses: actions/checkout@93ea575cb5d8a053eaa0ac8fa3b40d7e05a33cc8 # v3.1.0
diff --git a/.github/workflows/deps.yml b/.github/workflows/deps.yml
index ecf119d..485246c 100644
--- a/.github/workflows/deps.yml
+++ b/.github/workflows/deps.yml
@@ -11,7 +11,7 @@ jobs:
       - name: Install Go
         uses: actions/setup-go@c4a742cab115ed795e34d4513e2cf7d472deb55f # v3.3.1
         with:
-          go-version: 1.19.x
+          go-version: 1.20.x
       - name: Checkout code
         uses: actions/checkout@93ea575cb5d8a053eaa0ac8fa3b40d7e05a33cc8 # v3.1.0
         with:
diff --git a/.github/workflows/metadata.yml b/.github/workflows/metadata.yml
index 81b08fb..d1b3b92 100644
--- a/.github/workflows/metadata.yml
+++ b/.github/workflows/metadata.yml
@@ -12,7 +12,7 @@ jobs:
       - name: Install Go
         uses: actions/setup-go@c4a742cab115ed795e34d4513e2cf7d472deb55f # v3.3.1
         with:
-          go-version: 1.19.x
+          go-version: 1.20.x
       - name: Checkout code
         uses: actions/checkout@93ea575cb5d8a053eaa0ac8fa3b40d7e05a33cc8 # v3.1.0
         with:
diff --git a/.github/workflows/packages.yml b/.github/workflows/packages.yml
index 8cfbe4b..d371d3e 100644
--- a/.github/workflows/packages.yml
+++ b/.github/workflows/packages.yml
@@ -15,7 +15,7 @@ jobs:
       - name: Install Go
         uses: actions/setup-go@c4a742cab115ed795e34d4513e2cf7d472deb55f # v3.3.1
         with:
-          go-version: 1.19.x
+          go-version: 1.20.x
           check-latest: true
       - name: Checkout avo
         uses: actions/checkout@93ea575cb5d8a053eaa0ac8fa3b40d7e05a33cc8 # v3.1.0
@@ -52,7 +52,7 @@ jobs:
       - name: Install Go
         uses: actions/setup-go@c4a742cab115ed795e34d4513e2cf7d472deb55f # v3.3.1
         with:
-          go-version: 1.19.x
+          go-version: 1.20.x
           check-latest: true
       - name: Checkout avo
         uses: actions/checkout@93ea575cb5d8a053eaa0ac8fa3b40d7e05a33cc8 # v3.1.0
@@ -98,7 +98,7 @@ jobs:
       - name: Install Go
         uses: actions/setup-go@c4a742cab115ed795e34d4513e2cf7d472deb55f # v3.3.1
         with:
-          go-version: 1.19.x
+          go-version: 1.20.x
           check-latest: true
       - name: Checkout avo
         uses: actions/checkout@93ea575cb5d8a053eaa0ac8fa3b40d7e05a33cc8 # v3.1.0
@@ -145,7 +145,7 @@ jobs:
       - name: Install Go
         uses: actions/setup-go@c4a742cab115ed795e34d4513e2cf7d472deb55f # v3.3.1
         with:
-          go-version: 1.19.x
+          go-version: 1.20.x
           check-latest: true
       - name: Checkout avo
         uses: actions/checkout@93ea575cb5d8a053eaa0ac8fa3b40d7e05a33cc8 # v3.1.0
@@ -180,7 +180,7 @@ jobs:
       - name: Install Go
         uses: actions/setup-go@c4a742cab115ed795e34d4513e2cf7d472deb55f # v3.3.1
         with:
-          go-version: 1.19.x
+          go-version: 1.20.x
           check-latest: true
       - name: Checkout avo
         uses: actions/checkout@93ea575cb5d8a053eaa0ac8fa3b40d7e05a33cc8 # v3.1.0
@@ -217,7 +217,7 @@ jobs:
       - name: Install Go
         uses: actions/setup-go@c4a742cab115ed795e34d4513e2cf7d472deb55f # v3.3.1
         with:
-          go-version: 1.19.x
+          go-version: 1.20.x
           check-latest: true
       - name: Checkout avo
         uses: actions/checkout@93ea575cb5d8a053eaa0ac8fa3b40d7e05a33cc8 # v3.1.0
@@ -252,7 +252,7 @@ jobs:
       - name: Install Go
         uses: actions/setup-go@c4a742cab115ed795e34d4513e2cf7d472deb55f # v3.3.1
         with:
-          go-version: 1.19.x
+          go-version: 1.20.x
           check-latest: true
       - name: Checkout avo
         uses: actions/checkout@93ea575cb5d8a053eaa0ac8fa3b40d7e05a33cc8 # v3.1.0
@@ -290,7 +290,7 @@ jobs:
       - name: Install Go
         uses: actions/setup-go@c4a742cab115ed795e34d4513e2cf7d472deb55f # v3.3.1
         with:
-          go-version: 1.19.x
+          go-version: 1.20.x
           check-latest: true
       - name: Checkout avo
         uses: actions/checkout@93ea575cb5d8a053eaa0ac8fa3b40d7e05a33cc8 # v3.1.0
@@ -325,7 +325,7 @@ jobs:
       - name: Install Go
         uses: actions/setup-go@c4a742cab115ed795e34d4513e2cf7d472deb55f # v3.3.1
         with:
-          go-version: 1.19.x
+          go-version: 1.20.x
           check-latest: true
       - name: Checkout avo
         uses: actions/checkout@93ea575cb5d8a053eaa0ac8fa3b40d7e05a33cc8 # v3.1.0
@@ -360,7 +360,7 @@ jobs:
       - name: Install Go
         uses: actions/setup-go@c4a742cab115ed795e34d4513e2cf7d472deb55f # v3.3.1
         with:
-          go-version: 1.19.x
+          go-version: 1.20.x
           check-latest: true
       - name: Checkout avo
         uses: actions/checkout@93ea575cb5d8a053eaa0ac8fa3b40d7e05a33cc8 # v3.1.0
@@ -410,7 +410,7 @@ jobs:
       - name: Install Go
         uses: actions/setup-go@c4a742cab115ed795e34d4513e2cf7d472deb55f # v3.3.1
         with:
-          go-version: 1.19.x
+          go-version: 1.20.x
           check-latest: true
       - name: Checkout avo
         uses: actions/checkout@93ea575cb5d8a053eaa0ac8fa3b40d7e05a33cc8 # v3.1.0
@@ -461,7 +461,7 @@ jobs:
       - name: Install Go
         uses: actions/setup-go@c4a742cab115ed795e34d4513e2cf7d472deb55f # v3.3.1
         with:
-          go-version: 1.19.x
+          go-version: 1.20.x
           check-latest: true
       - name: Checkout avo
         uses: actions/checkout@93ea575cb5d8a053eaa0ac8fa3b40d7e05a33cc8 # v3.1.0
@@ -514,7 +514,7 @@ jobs:
       - name: Install Go
         uses: actions/setup-go@c4a742cab115ed795e34d4513e2cf7d472deb55f # v3.3.1
         with:
-          go-version: 1.19.x
+          go-version: 1.20.x
           check-latest: true
       - name: Checkout avo
         uses: actions/checkout@93ea575cb5d8a053eaa0ac8fa3b40d7e05a33cc8 # v3.1.0
@@ -567,7 +567,7 @@ jobs:
       - name: Install Go
         uses: actions/setup-go@c4a742cab115ed795e34d4513e2cf7d472deb55f # v3.3.1
         with:
-          go-version: 1.19.x
+          go-version: 1.20.x
           check-latest: true
       - name: Checkout avo
         uses: actions/checkout@93ea575cb5d8a053eaa0ac8fa3b40d7e05a33cc8 # v3.1.0
@@ -612,7 +612,7 @@ jobs:
       - name: Install Go
         uses: actions/setup-go@c4a742cab115ed795e34d4513e2cf7d472deb55f # v3.3.1
         with:
-          go-version: 1.19.x
+          go-version: 1.20.x
           check-latest: true
       - name: Checkout avo
         uses: actions/checkout@93ea575cb5d8a053eaa0ac8fa3b40d7e05a33cc8 # v3.1.0
@@ -647,7 +647,7 @@ jobs:
       - name: Install Go
         uses: actions/setup-go@c4a742cab115ed795e34d4513e2cf7d472deb55f # v3.3.1
         with:
-          go-version: 1.19.x
+          go-version: 1.20.x
           check-latest: true
       - name: Checkout avo
         uses: actions/checkout@93ea575cb5d8a053eaa0ac8fa3b40d7e05a33cc8 # v3.1.0
@@ -684,7 +684,7 @@ jobs:
       - name: Install Go
         uses: actions/setup-go@c4a742cab115ed795e34d4513e2cf7d472deb55f # v3.3.1
         with:
-          go-version: 1.19.x
+          go-version: 1.20.x
           check-latest: true
       - name: Checkout avo
         uses: actions/checkout@93ea575cb5d8a053eaa0ac8fa3b40d7e05a33cc8 # v3.1.0
@@ -721,7 +721,7 @@ jobs:
       - name: Install Go
         uses: actions/setup-go@c4a742cab115ed795e34d4513e2cf7d472deb55f # v3.3.1
         with:
-          go-version: 1.19.x
+          go-version: 1.20.x
           check-latest: true
       - name: Checkout avo
         uses: actions/checkout@93ea575cb5d8a053eaa0ac8fa3b40d7e05a33cc8 # v3.1.0
@@ -756,7 +756,7 @@ jobs:
       - name: Install Go
         uses: actions/setup-go@c4a742cab115ed795e34d4513e2cf7d472deb55f # v3.3.1
         with:
-          go-version: 1.19.x
+          go-version: 1.20.x
           check-latest: true
       - name: Checkout avo
         uses: actions/checkout@93ea575cb5d8a053eaa0ac8fa3b40d7e05a33cc8 # v3.1.0
@@ -791,7 +791,7 @@ jobs:
       - name: Install Go
         uses: actions/setup-go@c4a742cab115ed795e34d4513e2cf7d472deb55f # v3.3.1
         with:
-          go-version: 1.19.x
+          go-version: 1.20.x
           check-latest: true
       - name: Checkout avo
         uses: actions/checkout@93ea575cb5d8a053eaa0ac8fa3b40d7e05a33cc8 # v3.1.0
@@ -826,7 +826,7 @@ jobs:
       - name: Install Go
         uses: actions/setup-go@c4a742cab115ed795e34d4513e2cf7d472deb55f # v3.3.1
         with:
-          go-version: 1.19.x
+          go-version: 1.20.x
           check-latest: true
       - name: Checkout avo
         uses: actions/checkout@93ea575cb5d8a053eaa0ac8fa3b40d7e05a33cc8 # v3.1.0
@@ -861,7 +861,7 @@ jobs:
       - name: Install Go
         uses: actions/setup-go@c4a742cab115ed795e34d4513e2cf7d472deb55f # v3.3.1
         with:
-          go-version: 1.19.x
+          go-version: 1.20.x
           check-latest: true
       - name: Checkout avo
         uses: actions/checkout@93ea575cb5d8a053eaa0ac8fa3b40d7e05a33cc8 # v3.1.0
@@ -901,7 +901,7 @@ jobs:
       - name: Install Go
         uses: actions/setup-go@c4a742cab115ed795e34d4513e2cf7d472deb55f # v3.3.1
         with:
-          go-version: 1.19.x
+          go-version: 1.20.x
           check-latest: true
       - name: Checkout avo
         uses: actions/checkout@93ea575cb5d8a053eaa0ac8fa3b40d7e05a33cc8 # v3.1.0
@@ -936,7 +936,7 @@ jobs:
       - name: Install Go
         uses: actions/setup-go@c4a742cab115ed795e34d4513e2cf7d472deb55f # v3.3.1
         with:
-          go-version: 1.19.x
+          go-version: 1.20.x
           check-latest: true
       - name: Checkout avo
         uses: actions/checkout@93ea575cb5d8a053eaa0ac8fa3b40d7e05a33cc8 # v3.1.0
@@ -974,7 +974,7 @@ jobs:
       - name: Install Go
         uses: actions/setup-go@c4a742cab115ed795e34d4513e2cf7d472deb55f # v3.3.1
         with:
-          go-version: 1.19.x
+          go-version: 1.20.x
           check-latest: true
       - name: Checkout avo
         uses: actions/checkout@93ea575cb5d8a053eaa0ac8fa3b40d7e05a33cc8 # v3.1.0
@@ -1012,7 +1012,7 @@ jobs:
       - name: Install Go
         uses: actions/setup-go@c4a742cab115ed795e34d4513e2cf7d472deb55f # v3.3.1
         with:
-          go-version: 1.19.x
+          go-version: 1.20.x
           check-latest: true
       - name: Checkout avo
         uses: actions/checkout@93ea575cb5d8a053eaa0ac8fa3b40d7e05a33cc8 # v3.1.0
@@ -1047,7 +1047,7 @@ jobs:
       - name: Install Go
         uses: actions/setup-go@c4a742cab115ed795e34d4513e2cf7d472deb55f # v3.3.1
         with:
-          go-version: 1.19.x
+          go-version: 1.20.x
           check-latest: true
       - name: Checkout avo
         uses: actions/checkout@93ea575cb5d8a053eaa0ac8fa3b40d7e05a33cc8 # v3.1.0
@@ -1082,7 +1082,7 @@ jobs:
       - name: Install Go
         uses: actions/setup-go@c4a742cab115ed795e34d4513e2cf7d472deb55f # v3.3.1
         with:
-          go-version: 1.19.x
+          go-version: 1.20.x
           check-latest: true
       - name: Checkout avo
         uses: actions/checkout@93ea575cb5d8a053eaa0ac8fa3b40d7e05a33cc8 # v3.1.0
diff --git a/.github/workflows/stress.yml b/.github/workflows/stress.yml
index c019a59..a83ef80 100644
--- a/.github/workflows/stress.yml
+++ b/.github/workflows/stress.yml
@@ -13,7 +13,7 @@ jobs:
       - name: Install Go
         uses: actions/setup-go@c4a742cab115ed795e34d4513e2cf7d472deb55f # v3.3.1
         with:
-          go-version: 1.19.x
+          go-version: 1.20.x
           check-latest: true
       - name: Checkout code
         uses: actions/checkout@93ea575cb5d8a053eaa0ac8fa3b40d7e05a33cc8 # v3.1.0
diff --git a/.github/workflows/thirdparty.yml b/.github/workflows/thirdparty.yml
index c765279..d7c47c0 100644
--- a/.github/workflows/thirdparty.yml
+++ b/.github/workflows/thirdparty.yml
@@ -18,7 +18,7 @@ jobs:
       - name: Install Go
         uses: actions/setup-go@c4a742cab115ed795e34d4513e2cf7d472deb55f # v3.3.1
         with:
-          go-version: 1.19.x
+          go-version: 1.20.x
           check-latest: true
       - name: Checkout code
         uses: actions/checkout@93ea575cb5d8a053eaa0ac8fa3b40d7e05a33cc8 # v3.1.0
diff --git a/.golangci.yml b/.golangci.yml
index 1e4894a..a4dcd1c 100644
--- a/.golangci.yml
+++ b/.golangci.yml
@@ -5,6 +5,7 @@ linters:
   disable:
     - cyclop
     - deadcode
+    - dupword
     - errname
     - exhaustruct
     - exhaustivestruct
diff --git a/gotypes/signature_test.go b/gotypes/signature_test.go
index 03f8e9b..07a95c5 100644
--- a/gotypes/signature_test.go
+++ b/gotypes/signature_test.go
@@ -3,7 +3,7 @@ package gotypes
 import (
 	"go/token"
 	"go/types"
-	"strings"
+	"regexp"
 	"testing"
 
 	"golang.org/x/tools/go/packages"
@@ -118,17 +118,22 @@ func TestParseSignature(t *testing.T) {
 
 func TestParseSignatureErrors(t *testing.T) {
 	cases := []struct {
-		Expr          string
-		ErrorContains string
+		Expr         string
+		ErrorPattern string
 	}{
-		{"idkjklol", "undeclared name"},
-		{"struct{}", "not a function signature"},
-		{"uint32(0xfeedbeef)", "should have nil value"},
+		{"idkjklol", `(undeclared|undefined)`}, // error message changed in go 1.20
+		{"struct{}", `not a function signature`},
+		{"uint32(0xfeedbeef)", `should have nil value`},
 	}
 	for _, c := range cases {
+		errrx, err := regexp.Compile(c.ErrorPattern)
+		if err != nil {
+			t.Fatal(err)
+		}
+
 		s, err := ParseSignature(c.Expr)
-		if s != nil || err == nil || !strings.Contains(err.Error(), c.ErrorContains) {
-			t.Errorf("expect error from expression %s\ngot: %s\nexpect substring: %s\n", c.Expr, err, c.ErrorContains)
+		if s != nil || err == nil || !errrx.MatchString(err.Error()) {
+			t.Errorf("expect error from expression %s\ngot: %s\nexpect match: %s\n", c.Expr, err, c.ErrorPattern)
 		}
 	}
 }
diff --git a/internal/gen/mov.go b/internal/gen/mov.go
index c4e3cd0..0b1ec1e 100644
--- a/internal/gen/mov.go
+++ b/internal/gen/mov.go
@@ -17,7 +17,7 @@ type mov struct {
 }
 
 // NewMOV generates a function that will auto-select the correct MOV instruction
-// based on operand types and and sizes.
+// based on operand types and sizes.
 func NewMOV(cfg printer.Config) Interface {
 	return GoFmt(&mov{cfg: cfg})
 }
diff --git a/script/bootstrap b/script/bootstrap
index 6b6b135..64090e6 100755
--- a/script/bootstrap
+++ b/script/bootstrap
@@ -4,16 +4,13 @@
 go install ./internal/cmd/asmvet
 
 # golangci-lint for linting
-golangci_lint_version='v1.49.0'
+golangci_lint_version='v1.51.2'
 golangci_install_script="https://raw.githubusercontent.com/golangci/golangci-lint/${golangci_lint_version}/install.sh"
 curl -sfL "${golangci_install_script}" | sh -s -- -b "$(go env GOPATH)/bin" "${golangci_lint_version}"
 
 # embedmd required for documentation generation
 go install github.com/campoy/embedmd@v1.0.0
 
-# covertool for merging coverage reports
-go install github.com/dlespiau/covertool@v0.0.0-20180314162135-b0c4c6d0583a
-
 # asmfmt for enforcing assembly style
 go install github.com/klauspost/asmfmt/cmd/asmfmt@v1.3.2
 
diff --git a/script/coverage b/script/coverage
index 136a51f..db0d874 100755
--- a/script/coverage
+++ b/script/coverage
@@ -1,7 +1,17 @@
-#!/bin/bash -ex
+#!/bin/bash
+
+set -euo pipefail
 
 ext=".coverprofile"
 
+# Temporary working directory.
+workdir=$(mktemp -d)
+
+function cleanup() {
+    rm -rf "${workdir}"
+}
+trap cleanup EXIT
+
 # Clean existing coverage files.
 find . -name '*'${ext} | xargs rm -f
 
@@ -9,16 +19,27 @@ find . -name '*'${ext} | xargs rm -f
 go test -covermode=count -coverprofile=unittests${ext} ./...
 
 # Integration test coverage.
-coverprofiles=()
+#
+# Collect for each individual avo assembly generator.
+coverbase="${workdir}/cover"
+coversingle="${coverbase}/test"
+mkdir -p "${coversingle}"
+
+coverdirs=()
 for main in $(find . -name 'asm.go'); do
 	dir=$(dirname ${main})
 	name=$(basename ${dir})
-	coverprofile="${dir}/${name}${ext}"
-	./script/covermain ${main} ${coverprofile} > /dev/null
-	coverprofiles+=(${coverprofile})
+
+	coverdir="${coversingle}/${name}"
+	mkdir "${coverdir}"
+	GOCOVERDIR="${coverdir}" go run -tags=integration -cover "${main}" -out /dev/null
+
+	coverdirs+=("${coverdir}")
 done
 
-covertool merge --output integration${ext} ${coverprofiles[@]}
-
-# Merge.
-covertool merge --output all${ext} unittests${ext} integration${ext}
+# Merge integration test coverage.
+covermergeinputs=$(IFS=","; echo "${coverdirs[*]}")
+covermergeoutput="${coverbase}/merge"
+mkdir "${covermergeoutput}"
+go tool covdata merge -i="${covermergeinputs}" -o="${covermergeoutput}"
+go tool covdata textfmt -i="${covermergeoutput}" -o="integration${ext}"
diff --git a/script/covermain b/script/covermain
deleted file mode 100755
index 5afbd1e..0000000
--- a/script/covermain
+++ /dev/null
@@ -1,29 +0,0 @@
-#!/bin/bash -e
-
-main=$1
-coverprofile=$2
-
-# Temporary working directory.
-workdir=$(mktemp -d tmpXXXXXXXX)
-
-# Wrap the main function in a go test.
-cp ${main} ${workdir}
-cat > ${workdir}/main_test.go <<EOF
-package main
-
-import "testing"
-
-func TestRunMain(t *testing.T) {
-	main()
-}
-EOF
-
-# Execute the test with coverage.
-testbin="${workdir}/testbin"
-output="${workdir}/cover.out"
-go test -tags=integration -o ${testbin} -covermode=count -coverpkg="github.com/mmcloughlin/avo/..." ${workdir}/*.go
-${testbin} -test.coverprofile=${output}
-cp ${output} ${coverprofile}
-
-# Cleanup.
-rm -rf ${workdir}
diff --git a/tests/thirdparty/make_workflow.go b/tests/thirdparty/make_workflow.go
index 5a81709..39dcc56 100644
--- a/tests/thirdparty/make_workflow.go
+++ b/tests/thirdparty/make_workflow.go
@@ -102,7 +102,7 @@ func GenerateWorkflow(s *thirdparty.Suite) ([]byte, error) {
 		g.Linef("- name: Install Go")
 		g.Linef("  uses: actions/setup-go@c4a742cab115ed795e34d4513e2cf7d472deb55f # v3.3.1")
 		g.Linef("  with:")
-		g.Linef("    go-version: 1.19.x")
+		g.Linef("    go-version: 1.20.x")
 		g.Linef("    check-latest: true")
 
 		// Checkout avo.