diff --git a/src/cmd/go/pkg.go b/src/cmd/go/pkg.go
index 307bd74cf1..345d8fb54b 100644
--- a/src/cmd/go/pkg.go
+++ b/src/cmd/go/pkg.go
@@ -671,7 +671,12 @@ func packagesAndErrors(args []string) []*Package {
 	args = importPaths(args)
 	var pkgs []*Package
 	var stk importStack
+	var set = make(map[string]bool)
+
 	for _, arg := range args {
+		set[arg] = true
+	}
+	for arg := range set {
 		pkgs = append(pkgs, loadPackage(arg, &stk))
 	}
 
diff --git a/src/cmd/go/test.bash b/src/cmd/go/test.bash
index 82cbd389cf..e88610cfe8 100755
--- a/src/cmd/go/test.bash
+++ b/src/cmd/go/test.bash
@@ -136,6 +136,12 @@ if GOPATH=:$(pwd)/testdata:. ./testgo build go-cmd-test; then
     ok=false
 fi
 
+# issue 4104
+if [ $(./testgo test fmt fmt fmt fmt fmt | wc -l) -ne 1 ] ; then
+    echo 'go test fmt fmt fmt fmt fmt tested the same package multiple times'
+    ok=false
+fi
+
 if $ok; then
 	echo PASS
 else