diff --git a/cmd/cloud_sql_proxy/proxy.go b/cmd/cloud_sql_proxy/proxy.go
index 2c3358e08..2e6ebf849 100644
--- a/cmd/cloud_sql_proxy/proxy.go
+++ b/cmd/cloud_sql_proxy/proxy.go
@@ -227,15 +227,28 @@ func parseInstanceConfig(dir, instance string, cl *http.Client) (instanceConfig,
 			ret.Address = fmt.Sprintf("%s:%s", spl[1], spl[2])
 		}
 	} else {
+		sql, err := sqladmin.New(cl)
+		if err != nil {
+			return instanceConfig{}, err
+		}
+
 		ret.Instance = instance
 		// Default to unix socket.
 		ret.Network = "unix"
 		spl := strings.SplitN(instance, ":", 3)
-		sql, err := sqladmin.New(cl)
-		if err != nil {
-			return instanceConfig{}, err
+
+		var proj, name string
+		if len(spl) < 2 {
+			return instanceConfig{}, fmt.Errorf("invalid instance name: must be in the form `project:region:instance-name`; invalid name was %q", instance)
+		} else if len(spl) == 2 {
+			// We allow people to omit the region due to historical reasons. It'll
+			// fail later in the code if this isn't allowed, so just assume it's
+			// allowed until we actually need the region in this API call.
+			proj, name = spl[0], spl[1]
+		} else { // if len(spl) == 3
+			proj, name = spl[0], spl[2]
 		}
-		in, err := sql.Instances.Get(spl[0], spl[2]).Do()
+		in, err := sql.Instances.Get(proj, name).Do()
 		if err != nil {
 			return instanceConfig{}, err
 		}
diff --git a/cmd/cloud_sql_proxy/proxy_test.go b/cmd/cloud_sql_proxy/proxy_test.go
index 3153daf73..bdbf50ff1 100644
--- a/cmd/cloud_sql_proxy/proxy_test.go
+++ b/cmd/cloud_sql_proxy/proxy_test.go
@@ -51,28 +51,28 @@ func TestCreateInstanceConfigs(t *testing.T) {
 			"", true, nil, "", true,
 		}, {
 			"setting -fuse, -dir, and -instances",
-			"dir", true, []string{"x"}, "", true,
+			"dir", true, []string{"proj:reg:x"}, "", true,
 		}, {
 			"setting -fuse, -dir, and -instances_metadata",
 			"dir", true, nil, "md", true,
 		}, {
 			"setting -dir and -instances (unix socket)",
-			"dir", false, []string{"x"}, "", false,
+			"dir", false, []string{"proj:reg:x"}, "", false,
 		}, {
 			"Seting -instance (unix socket)",
-			"", false, []string{"x"}, "", true,
+			"", false, []string{"proj:reg:x"}, "", true,
 		}, {
 			"setting -instance (tcp socket)",
-			"", false, []string{"x=tcp:1234"}, "", false,
+			"", false, []string{"proj:reg:x=tcp:1234"}, "", false,
 		}, {
 			"setting -instance (tcp socket) and -instances_metadata",
-			"", false, []string{"x=tcp:1234"}, "md", true,
+			"", false, []string{"proj:reg:x=tcp:1234"}, "md", true,
 		}, {
 			"setting -dir, -instance (tcp socket), and -instances_metadata",
-			"dir", false, []string{"x=tcp:1234"}, "md", false,
+			"dir", false, []string{"proj:reg:x=tcp:1234"}, "md", false,
 		}, {
 			"setting -dir, -instance (unix socket), and -instances_metadata",
-			"dir", false, []string{"x"}, "md", false,
+			"dir", false, []string{"proj:reg:x"}, "md", false,
 		}, {
 			"setting -dir and -instances_metadata",
 			"dir", false, nil, "md", false,
@@ -103,31 +103,31 @@ func TestParseInstanceConfig(t *testing.T) {
 		wantErr bool
 	}{
 		{
-			"/x", "my-instance",
-			instanceConfig{"my-instance", "unix", "/x/my-instance"},
+			"/x", "my-proj:my-reg:my-instance",
+			instanceConfig{"my-proj:my-reg:my-instance", "unix", "/x/my-proj:my-reg:my-instance"},
 			false,
 		}, {
-			"/x", "my-instance=tcp:1234",
-			instanceConfig{"my-instance", "tcp", "127.0.0.1:1234"},
+			"/x", "my-proj:my-reg:my-instance=tcp:1234",
+			instanceConfig{"my-proj:my-reg:my-instance", "tcp", "127.0.0.1:1234"},
 			false,
 		}, {
-			"/x", "my-instance=tcp:my-host:1111",
-			instanceConfig{"my-instance", "tcp", "my-host:1111"},
+			"/x", "my-proj:my-reg:my-instance=tcp:my-host:1111",
+			instanceConfig{"my-proj:my-reg:my-instance", "tcp", "my-host:1111"},
 			false,
 		}, {
-			"/x", "my-instance=",
+			"/x", "my-proj:my-reg:my-instance=",
 			instanceConfig{},
 			true,
 		}, {
-			"/x", "my-instance=cool network",
+			"/x", "my-proj:my-reg:my-instance=cool network",
 			instanceConfig{},
 			true,
 		}, {
-			"/x", "my-instance=cool network:1234",
+			"/x", "my-proj:my-reg:my-instance=cool network:1234",
 			instanceConfig{},
 			true,
 		}, {
-			"/x", "my-instance=oh:so:many:colons",
+			"/x", "my-proj:my-reg:my-instance=oh:so:many:colons",
 			instanceConfig{},
 			true,
 		},
@@ -138,6 +138,9 @@ func TestParseInstanceConfig(t *testing.T) {
 				t.Errorf("parseInstanceConfig(%s, %s) = %+v, wanted error", got)
 			}
 			continue
+		} else if err != nil {
+			t.Errorf("parseInstanceConfig(%s, %s) had unexpected error: %v", v.dir, v.instance, err)
+			continue
 		}
 		if got != v.wantCfg {
 			t.Errorf("parseInstanceConfig(%s, %s) = %+v, want %+v", v.dir, v.instance, got, v.wantCfg)