diff --git a/go/buildutil/allpackages.go b/go/buildutil/allpackages.go
index 4d4366c1..c0cb03e7 100644
--- a/go/buildutil/allpackages.go
+++ b/go/buildutil/allpackages.go
@@ -137,6 +137,9 @@ func allPackages(ctxt *build.Context, root string, ch chan<- item) {
 //
 // 	encoding/... -encoding/xml
 //
+// A trailing slash in a pattern is ignored.  (Path components of Go
+// package names are separated by slash, not the platform's path separator.)
+//
 func ExpandPatterns(ctxt *build.Context, patterns []string) map[string]bool {
 	// TODO(adonovan): support other features of 'go list':
 	// - "std"/"cmd"/"all" meta-packages
@@ -187,7 +190,7 @@ func ExpandPatterns(ctxt *build.Context, patterns []string) map[string]bool {
 			}
 		} else {
 			// single package
-			doPkg(arg, neg)
+			doPkg(strings.TrimSuffix(arg, "/"), neg)
 		}
 	}
 
diff --git a/go/buildutil/allpackages_test.go b/go/buildutil/allpackages_test.go
index 96bf77a6..0440ff24 100644
--- a/go/buildutil/allpackages_test.go
+++ b/go/buildutil/allpackages_test.go
@@ -61,6 +61,8 @@ func TestExpandPatterns(t *testing.T) {
 		{"...", "encoding encoding/hex encoding/json encoding/xml fmt"},
 		{"encoding/... -encoding/xml", "encoding encoding/hex encoding/json"},
 		{"... -encoding/...", "fmt"},
+		{"encoding", "encoding"},
+		{"encoding/", "encoding"},
 	} {
 		var pkgs []string
 		for pkg := range buildutil.ExpandPatterns(ctxt, strings.Fields(test.patterns)) {