diff --git a/cmd/gomobile/build_androidapp.go b/cmd/gomobile/build_androidapp.go
index d0d7955..06b2571 100644
--- a/cmd/gomobile/build_androidapp.go
+++ b/cmd/gomobile/build_androidapp.go
@@ -287,20 +287,15 @@
 // but not exactly same.
 func androidPkgName(name string) string {
 	var res []rune
-	for i, r := range name {
+	for _, r := range name {
 		switch {
-		case 'a' <= r && r <= 'z', 'A' <= r && r <= 'Z':
-			res = append(res, r)
-		case '0' <= r && r <= '9':
-			if i == 0 {
-				panic(fmt.Sprintf("package name %q is not a valid go package name", name))
-			}
+		case 'a' <= r && r <= 'z', 'A' <= r && r <= 'Z', '0' <= r && r <= '9':
 			res = append(res, r)
 		default:
 			res = append(res, '_')
 		}
 	}
-	if len(res) == 0 || res[0] == '_' {
+	if len(res) == 0 || res[0] == '_' || ('0' <= res[0] && res[0] <= '9') {
 		// Android does not seem to allow the package part starting with _.
 		res = append([]rune{'g', 'o'}, res...)
 	}
diff --git a/cmd/gomobile/build_test.go b/cmd/gomobile/build_test.go
index 5b4358d..f353f7b 100644
--- a/cmd/gomobile/build_test.go
+++ b/cmd/gomobile/build_test.go
@@ -54,6 +54,7 @@
 		{".-.", "go___"},
 		{"abstract", "abstract_"},
 		{"Abstract", "Abstract"},
+		{"12345", "go12345"},
 	}
 
 	for _, tc := range tests {