diff --git a/src/aarch64/ffi.c b/src/aarch64/ffi.c
index cf33abc2..8ec9c390 100644
--- a/src/aarch64/ffi.c
+++ b/src/aarch64/ffi.c
@@ -316,7 +316,7 @@ extend_integer_type (void *source, int type)
 static void
 extend_hfa_type (void *dest, void *src, int h)
 {
-  int f = h - AARCH64_RET_S4;
+  ssize_t f = h - AARCH64_RET_S4;
   void *x0;
 
   asm volatile (