diff --git a/script/lib.sh b/script/lib.sh
new file mode 100644
index 0000000..5941302
--- /dev/null
+++ b/script/lib.sh
@@ -0,0 +1,6 @@
+# Print an error message to the terminal.
+print_error() {
+    local red='\033[0;31m'
+    local nocolor='\033[0m'
+    printf "${red}error${nocolor}\t$1\n"
+}
diff --git a/script/lint b/script/lint
index 3a63ab7..fe8922a 100755
--- a/script/lint
+++ b/script/lint
@@ -15,3 +15,6 @@ golangci-lint run ./... ./examples/...
 
 # Check asm declarations.
 asmdecl ./...
+
+# Custom linters.
+./script/linter/pkgdoc
diff --git a/script/linter/pkgdoc b/script/linter/pkgdoc
new file mode 100755
index 0000000..fa7c50a
--- /dev/null
+++ b/script/linter/pkgdoc
@@ -0,0 +1,12 @@
+#!/bin/bash -e
+
+source script/lib.sh
+
+status=0
+pkgs=$(go list -f '{{if not .Doc}}{{.ImportPath}}{{end}}' ./...)
+for pkg in ${pkgs}; do
+    print_error "${pkg} missing docstring"
+    status=1
+done
+
+exit ${status}
diff --git a/tests/fixedbugs/issue50/doc.go b/tests/fixedbugs/issue50/doc.go
new file mode 100644
index 0000000..946deaf
--- /dev/null
+++ b/tests/fixedbugs/issue50/doc.go
@@ -0,0 +1,2 @@
+// Package issue50 tests for 32-bit MOVD/MOVQ instruction forms.
+package issue50