diff --git a/android/OldPhoneNumberUtils.cpp b/android/OldPhoneNumberUtils.cpp
index 5f180dc..9c2f20e 100644
--- a/android/OldPhoneNumberUtils.cpp
+++ b/android/OldPhoneNumberUtils.cpp
@@ -173,7 +173,7 @@
  * is no such character in a.
  */
 static int indexOf(const char *a, char b) {
-    char *ix = strchr(a, b);
+    const char *ix = strchr(a, b);
 
     if (ix == NULL)
         return -1;