diff --git a/src/core/value.c b/src/core/value.c
index b54df0ce..b4a17dab 100644
--- a/src/core/value.c
+++ b/src/core/value.c
@@ -348,7 +348,7 @@ int32_t janet_hash(Janet x) {
                 hash = (int32_t)((hilo << 16) | (hilo >> 16));
             } else {
                 /* Assuming 4 byte pointer (or smaller) */
-                ptrdiff_t diff = ((char *)janet_unwrap_pointer(x) - (char *)0);
+                uintptr_t diff = janet_unwrap_pointer(x);
                 uint32_t hilo = (uint32_t) diff * 2654435769u;
                 hash = (int32_t)((hilo << 16) | (hilo >> 16));
             }