diff --git a/vm/os-unix.h b/vm/os-unix.h
index 97b1b39129..b2a1735fd7 100755
--- a/vm/os-unix.h
+++ b/vm/os-unix.h
@@ -23,6 +23,7 @@ typedef char F_SYMBOL;
 #define STRNCMP strncmp
 #define STRDUP strdup
 
+#define FIXNUM_FORMAT "%ld"
 #define CELL_FORMAT "%lu"
 #define CELL_HEX_FORMAT "%lx"
 
diff --git a/vm/os-windows.h b/vm/os-windows.h
index b12d677af2..af9b75bca5 100755
--- a/vm/os-windows.h
+++ b/vm/os-windows.h
@@ -20,13 +20,13 @@ typedef wchar_t F_CHAR;
 #define STRNCMP wcsncmp
 #define STRDUP _wcsdup
 
+#define FIXNUM_FORMAT "%Id"
+#define CELL_FORMAT "%lu"
+#define CELL_HEX_FORMAT "%Ix"
+
 #ifdef WIN64
-        #define CELL_FORMAT "%Iu"
-        #define CELL_HEX_FORMAT "%Ix"
 	#define CELL_HEX_PAD_FORMAT "%016Ix"
 #else
-        #define CELL_FORMAT "%lu"
-        #define CELL_HEX_FORMAT "%lx"
 	#define CELL_HEX_PAD_FORMAT "%08lx"
 #endif
 
diff --git a/vm/utilities.c b/vm/utilities.c
index 35fc7ad087..d97b540884 100755
--- a/vm/utilities.c
+++ b/vm/utilities.c
@@ -44,7 +44,7 @@ void print_cell_hex_pad(CELL x)
 
 void print_fixnum(F_FIXNUM x)
 {
-	printf(CELL_FORMAT,x);
+	printf(FIXNUM_FORMAT,x);
 }
 
 CELL read_cell_hex(void)