diff --git a/builder/remotecontext/git/gitutils.go b/builder/remotecontext/git/gitutils.go
index 77a45be..6213963 100644
--- a/builder/remotecontext/git/gitutils.go
+++ b/builder/remotecontext/git/gitutils.go
@@ -102,6 +102,11 @@
 		u.Fragment = ""
 		repo.remote = u.String()
 	}
+
+	if strings.HasPrefix(repo.ref, "-") {
+		return gitRepo{}, errors.Errorf("invalid refspec: %s", repo.ref)
+	}
+
 	return repo, nil
 }
 
@@ -124,7 +129,7 @@
 		args = append(args, "--depth", "1")
 	}
 
-	return append(args, "origin", ref)
+	return append(args, "origin", "--", ref)
 }
 
 // Check if a given git URL supports a shallow git clone,
diff --git a/builder/remotecontext/git/gitutils_test.go b/builder/remotecontext/git/gitutils_test.go
index 8c39679..34dd495 100644
--- a/builder/remotecontext/git/gitutils_test.go
+++ b/builder/remotecontext/git/gitutils_test.go
@@ -59,7 +59,7 @@
 	})
 
 	args := fetchArgs(serverURL.String(), "master")
-	exp := []string{"fetch", "--depth", "1", "origin", "master"}
+	exp := []string{"fetch", "--depth", "1", "origin", "--", "master"}
 	assert.Check(t, is.DeepEqual(exp, args))
 }
 
@@ -75,13 +75,13 @@
 	})
 
 	args := fetchArgs(serverURL.String(), "master")
-	exp := []string{"fetch", "origin", "master"}
+	exp := []string{"fetch", "origin", "--", "master"}
 	assert.Check(t, is.DeepEqual(exp, args))
 }
 
 func TestCloneArgsGit(t *testing.T) {
 	args := fetchArgs("git://github.com/docker/docker", "master")
-	exp := []string{"fetch", "--depth", "1", "origin", "master"}
+	exp := []string{"fetch", "--depth", "1", "origin", "--", "master"}
 	assert.Check(t, is.DeepEqual(exp, args))
 }
 
@@ -276,3 +276,18 @@
 		}
 	}
 }
+
+func TestGitInvalidRef(t *testing.T) {
+	gitUrls := []string{
+		"git://github.com/moby/moby#--foo bar",
+		"git@github.com/moby/moby#--upload-pack=sleep;:",
+		"git@g.com:a/b.git#-B",
+		"git@g.com:a/b.git#with space",
+	}
+
+	for _, url := range gitUrls {
+		_, err := Clone(url)
+		assert.Assert(t, err != nil)
+		assert.Check(t, is.Contains(strings.ToLower(err.Error()), "invalid refspec"))
+	}
+}