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diff --git a/c/raylib_bindings.c b/c/raylib_bindings.c
index a869c03..141ff1f 100644
--- a/c/raylib_bindings.c
+++ b/c/raylib_bindings.c
@@ -572,3 +572,7 @@ lean_obj_res setWindowState(uint64_t flags) {
   SetWindowState(flags);
   return IO_UNIT;
 }
+
+uint64_t lean_uint64_ctz(uint64_t x) {
+    return __builtin_ctzll(x);
+}
diff --git a/lean/Raylean/Core.lean b/lean/Raylean/Core.lean
index b1aa7ac..eb95702 100644
--- a/lean/Raylean/Core.lean
+++ b/lean/Raylean/Core.lean
@@ -179,3 +179,6 @@ def vsyncHint : UInt64 := 0x00000040
 def windowHighdpi : UInt64 := 0x00002000
 
 end Flags
+
+@[extern "lean_uint64_ctz"]
+opaque _root_.UInt64.ctz (x : UInt64) : UInt64