diff --git a/C/heapgc.c b/C/heapgc.c
index 152077526..c93b5813f 100644
--- a/C/heapgc.c
+++ b/C/heapgc.c
@@ -1256,7 +1256,7 @@ mark_variable(CELL_PTR current)
       goto begin;
 #ifdef DEBUG
     } else if (next < (CELL *)Yap_GlobalBase || next > (CELL *)Yap_TrailTop) {
-      fprintf(Yap_stderr, "OOPS in GC: marking, current=%p, *current=%lx next=%p\n", current, (unsigned long int)ccur, next);
+      fprintf(Yap_stderr, "OOPS in GC: marking, current=%p, *current=" UInt_FORMAT " next=%p\n", current, ccur, next);
 #endif
     } else {
 #ifdef COROUTING
@@ -1495,7 +1495,7 @@ mark_environments(CELL_PTR gc_ENV, OPREG size, CELL *pvbmap)
 
 #ifdef DEBUG
     if (size <  0 || size > 512)
-      fprintf(Yap_stderr,"OOPS in GC: env size for %p is %ld\n", gc_ENV, (unsigned long int)size);
+      fprintf(Yap_stderr,"OOPS in GC: env size for %p is " UInt_FORMAT "\n", gc_ENV, (CELL)size);
 #endif
     mark_db_fixed((CELL *)gc_ENV[E_CP]);
     /* for each saved variable */
diff --git a/H/Yap.h b/H/Yap.h
index 5598ef636..5c37b8a00 100644
--- a/H/Yap.h
+++ b/H/Yap.h
@@ -187,14 +187,14 @@
 /*   */ typedef unsigned int UInt;
 
 #define Int_FORMAT "%d"
-#define UInt_FORMAT "%ud"
+#define UInt_FORMAT "%u"
 
 #elif SIZEOF_LONG_INT==8
 /*   */ typedef long int Int;
 /*   */ typedef unsigned long int UInt;
 
 #define Int_FORMAT "%l"
-#define UInt_FORMAT "%ul"
+#define UInt_FORMAT "%lu"
 
 #   elif SIZEOF_LONG_LONG_INT==8
 /*   */ typedef long long int Int;