diff --git a/misc/cgo/testplugin/test.bash b/misc/cgo/testplugin/test.bash
index 69df5bd2bf..7e982c8961 100755
--- a/misc/cgo/testplugin/test.bash
+++ b/misc/cgo/testplugin/test.bash
@@ -27,8 +27,8 @@ GOPATH=$(pwd) go build -buildmode=plugin plugin1
 GOPATH=$(pwd) go build -buildmode=plugin plugin2
 GOPATH=$(pwd)/altpath go build -buildmode=plugin plugin-mismatch
 GOPATH=$(pwd) go build -buildmode=plugin -o=sub/plugin1.so sub/plugin1
-GOPATH=$(pwd) go build -buildmode=plugin unnamed1.go
-GOPATH=$(pwd) go build -buildmode=plugin unnamed2.go
+GOPATH=$(pwd) go build -buildmode=plugin -o=unnamed1.so unnamed1/main.go
+GOPATH=$(pwd) go build -buildmode=plugin -o=unnamed2.so unnamed2/main.go
 GOPATH=$(pwd) go build host
 
 LD_LIBRARY_PATH=$(pwd) ./host
diff --git a/misc/cgo/testplugin/unnamed1.go b/misc/cgo/testplugin/unnamed1/main.go
similarity index 100%
rename from misc/cgo/testplugin/unnamed1.go
rename to misc/cgo/testplugin/unnamed1/main.go
diff --git a/misc/cgo/testplugin/unnamed2.go b/misc/cgo/testplugin/unnamed2/main.go
similarity index 100%
rename from misc/cgo/testplugin/unnamed2.go
rename to misc/cgo/testplugin/unnamed2/main.go
diff --git a/src/cmd/go/internal/load/pkg.go b/src/cmd/go/internal/load/pkg.go
index be31ef5615..2f5a7a8018 100644
--- a/src/cmd/go/internal/load/pkg.go
+++ b/src/cmd/go/internal/load/pkg.go
@@ -1671,15 +1671,8 @@ func isStale(p *Package) (bool, string) {
 	return false, ""
 }
 
-// computeBuildID computes the build ID for p, leaving it in p.Internal.BuildID.
-// Build ID is a hash of the information we want to detect changes in.
-// See the long comment in isStale for details.
-func computeBuildID(p *Package) {
-	h := sha1.New()
-
-	// Include the list of files compiled as part of the package.
-	// This lets us detect removed files. See issue 3895.
-	inputFiles := str.StringList(
+func pkgInputFiles(p *Package) []string {
+	return str.StringList(
 		p.GoFiles,
 		p.CgoFiles,
 		p.CFiles,
@@ -1692,6 +1685,40 @@ func computeBuildID(p *Package) {
 		p.SwigFiles,
 		p.SwigCXXFiles,
 	)
+}
+
+// PluginPath computes the package path for a plugin main package.
+//
+// This is typically the import path of the main package p, unless the
+// plugin is being built directly from source files. In that case we
+// combine the package build ID with the contents of the main package
+// source files. This allows us to identify two different plugins
+// built from two source files with the same name.
+func PluginPath(p *Package) string {
+	if p.ImportPath != "command-line-arguments" {
+		return p.ImportPath
+	}
+	h := sha1.New()
+	fmt.Fprintf(h, "build ID: %s\n", p.Internal.BuildID)
+	for _, file := range str.StringList(p.GoFiles, p.CgoFiles, p.SFiles) {
+		data, err := ioutil.ReadFile(filepath.Join(p.Dir, file))
+		if err != nil {
+			base.Fatalf("go: %s", err)
+		}
+		h.Write(data)
+	}
+	return fmt.Sprintf("plugin/unnamed-%x", h.Sum(nil))
+}
+
+// computeBuildID computes the build ID for p, leaving it in p.Internal.BuildID.
+// Build ID is a hash of the information we want to detect changes in.
+// See the long comment in isStale for details.
+func computeBuildID(p *Package) {
+	h := sha1.New()
+
+	// Include the list of files compiled as part of the package.
+	// This lets us detect removed files. See issue 3895.
+	inputFiles := pkgInputFiles(p)
 	for _, file := range inputFiles {
 		fmt.Fprintf(h, "file %s\n", file)
 	}
diff --git a/src/cmd/go/internal/work/build.go b/src/cmd/go/internal/work/build.go
index 0395311ef6..6b9c511473 100644
--- a/src/cmd/go/internal/work/build.go
+++ b/src/cmd/go/internal/work/build.go
@@ -2200,9 +2200,7 @@ func (gcToolchain) gc(b *Builder, p *load.Package, archive, objdir string, asmhd
 
 	pkgpath := p.ImportPath
 	if cfg.BuildBuildmode == "plugin" {
-		if pkgpath == "command-line-arguments" {
-			pkgpath = "plugin/unnamed-" + p.Internal.BuildID
-		}
+		pkgpath = load.PluginPath(p)
 	} else if p.Name == "main" {
 		pkgpath = "main"
 	}
@@ -2536,11 +2534,7 @@ func (gcToolchain) ld(b *Builder, root *Action, out string, allactions []*Action
 		ldflags = append(ldflags, "-s", "-w")
 	}
 	if cfg.BuildBuildmode == "plugin" {
-		pluginpath := root.Package.ImportPath
-		if pluginpath == "command-line-arguments" {
-			pluginpath = "plugin/unnamed-" + root.Package.Internal.BuildID
-		}
-		ldflags = append(ldflags, "-pluginpath", pluginpath)
+		ldflags = append(ldflags, "-pluginpath", load.PluginPath(root.Package))
 	}
 
 	// If the user has not specified the -extld option, then specify the