diff --git a/gotypes/signature.go b/gotypes/signature.go
index e000020..ee514e3 100644
--- a/gotypes/signature.go
+++ b/gotypes/signature.go
@@ -97,20 +97,22 @@ func (s *Signature) init() {
 	p := s.sig.Params()
 	r := s.sig.Results()
 
-	// Compute parameter offsets.
+	// Compute parameter offsets. Note that if the function has results,
+	// additional padding up to max align is inserted between parameters and
+	// results.
 	vs := tuplevars(p)
 	vs = append(vs, types.NewParam(token.NoPos, nil, "sentinel", types.Typ[types.Uint64]))
 	paramsoffsets := Sizes.Offsetsof(vs)
 	paramssize := paramsoffsets[p.Len()]
+	if r.Len() == 0 {
+		paramssize = structsize(vs[:p.Len()])
+	}
 	s.params = newTuple(p, paramsoffsets, paramssize, "arg")
 
 	// Result offsets.
 	vs = tuplevars(r)
 	resultsoffsets := Sizes.Offsetsof(vs)
-	var resultssize int64
-	if n := len(vs); n > 0 {
-		resultssize = resultsoffsets[n-1] + Sizes.Sizeof(vs[n-1].Type())
-	}
+	resultssize := structsize(vs)
 	for i := range resultsoffsets {
 		resultsoffsets[i] += paramssize
 	}
@@ -175,3 +177,17 @@ func tuplevars(t *types.Tuple) []*types.Var {
 	}
 	return vs
 }
+
+// structsize computes the size of a struct containing the given variables as
+// fields. It would be equivalent to calculating the size of types.NewStruct(vs,
+// nil), apart from the fact that NewStruct panics if multiple fields have the
+// same name, and this happens for example if the variables represent return
+// types from a function.
+func structsize(vs []*types.Var) int64 {
+	n := len(vs)
+	if n == 0 {
+		return 0
+	}
+	offsets := Sizes.Offsetsof(vs)
+	return offsets[n-1] + Sizes.Sizeof(vs[n-1].Type())
+}
diff --git a/gotypes/signature_test.go b/gotypes/signature_test.go
index 91e688a..03997f1 100644
--- a/gotypes/signature_test.go
+++ b/gotypes/signature_test.go
@@ -159,6 +159,7 @@ func TestSignatureSizes(t *testing.T) {
 		{"func(uint64) uint64", 16},
 		{"func([7]byte) byte", 9},
 		{"func(uint64, uint64) (uint64, uint64)", 32},
+		{"func(uint16)", 2},
 	}
 	for _, c := range cases {
 		s, err := ParseSignature(c.Expr)
diff --git a/tests/fixedbugs/issue191/asm.go b/tests/fixedbugs/issue191/asm.go
new file mode 100644
index 0000000..f6373d5
--- /dev/null
+++ b/tests/fixedbugs/issue191/asm.go
@@ -0,0 +1,15 @@
+//go:build ignore
+// +build ignore
+
+package main
+
+import (
+	. "github.com/mmcloughlin/avo/build"
+)
+
+func main() {
+	TEXT("Uint16", 0, "func(n uint16)")
+	Doc("Uint16 tests argument size without return types.")
+	RET()
+	Generate()
+}
diff --git a/tests/fixedbugs/issue191/doc.go b/tests/fixedbugs/issue191/doc.go
new file mode 100644
index 0000000..f353ba0
--- /dev/null
+++ b/tests/fixedbugs/issue191/doc.go
@@ -0,0 +1,4 @@
+// Package issue191 tests for correct argument size for a function taking a
+// single uint16 argument. Prior to the fix, this test case triggered an asmdecl
+// error.
+package issue191
diff --git a/tests/fixedbugs/issue191/issue191.s b/tests/fixedbugs/issue191/issue191.s
new file mode 100644
index 0000000..8a2f927
--- /dev/null
+++ b/tests/fixedbugs/issue191/issue191.s
@@ -0,0 +1,5 @@
+// Code generated by command: go run asm.go -out issue191.s -stubs stub.go. DO NOT EDIT.
+
+// func Uint16(n uint16)
+TEXT ·Uint16(SB), $0-2
+	RET
diff --git a/tests/fixedbugs/issue191/issue191_test.go b/tests/fixedbugs/issue191/issue191_test.go
new file mode 100644
index 0000000..9fc1015
--- /dev/null
+++ b/tests/fixedbugs/issue191/issue191_test.go
@@ -0,0 +1,9 @@
+package issue191
+
+import "testing"
+
+//go:generate go run asm.go -out issue191.s -stubs stub.go
+
+func TestUint16(t *testing.T) {
+	Uint16(42)
+}
diff --git a/tests/fixedbugs/issue191/stub.go b/tests/fixedbugs/issue191/stub.go
new file mode 100644
index 0000000..5131b31
--- /dev/null
+++ b/tests/fixedbugs/issue191/stub.go
@@ -0,0 +1,6 @@
+// Code generated by command: go run asm.go -out issue191.s -stubs stub.go. DO NOT EDIT.
+
+package issue191
+
+// Uint16 tests argument size without return types.
+func Uint16(n uint16)