diff --git a/lib/flutter_libsparkmobile.dart b/lib/flutter_libsparkmobile.dart
index 14b43bf..260c562 100644
--- a/lib/flutter_libsparkmobile.dart
+++ b/lib/flutter_libsparkmobile.dart
@@ -542,11 +542,7 @@ abstract final class LibSpark {
     return hashes;
   }
 
-  /// [x] and [y] must be of length 64
   static String hashTag(String x, String y) {
-    assert(x.length == 64);
-    assert(y.length == 64);
-
     final xPtr = x.toNativeUtf8().cast<Char>();
     final yPtr = y.toNativeUtf8().cast<Char>();
 
diff --git a/src/flutter_libsparkmobile.cpp b/src/flutter_libsparkmobile.cpp
index 4da9416..473d750 100644
--- a/src/flutter_libsparkmobile.cpp
+++ b/src/flutter_libsparkmobile.cpp
@@ -369,7 +369,7 @@ const char* hashTag(const char* x, const char* y) {
     secp_primitives::GroupElement tag = secp_primitives::GroupElement(x, y, 16);
     uint256 hash = primitives::GetLTagHash(tag);
     std::string hex = hash.GetHex();
-    char* result = (char*) malloc(sizeof(char) * hex.length());
+    char* result = (char*) malloc(sizeof(char) * (hex.length() + 1));
     strcpy(result, hex.c_str());
     return result;
 }