diff --git a/src/if_py_both.h b/src/if_py_both.h
index 3380142..48137f1 100644
--- a/src/if_py_both.h
+++ b/src/if_py_both.h
@@ -5996,7 +5996,7 @@
     PyObject	*capsule;
     char	hexBuf[sizeof(void *) * 2 + 3];
 
-    sprintf(hexBuf, "%p", obj);
+    sprintf(hexBuf, "%p", (void *)obj);
 
 # ifdef PY_USE_CAPSULE
     capsule = PyDict_GetItemString(lookup_dict, hexBuf);