diff --git a/mongoose.h b/mongoose.h
index 422af564..a3648230 100644
--- a/mongoose.h
+++ b/mongoose.h
@@ -1945,7 +1945,7 @@ char *inet_ntoa(struct in_addr in);
 #include <stm32_sdk_hal.h>
 
 #define to64(x) strtoll(x, NULL, 10)
-#define INT64_FMT PRId64
+#define INT64_FMT "lld"
 #define SIZE_T_FMT "u"
 typedef struct stat cs_stat_t;
 #define DIRSEP '/'
diff --git a/src/common/platforms/platform_stm32.h b/src/common/platforms/platform_stm32.h
index 6b937569..d5b89192 100644
--- a/src/common/platforms/platform_stm32.h
+++ b/src/common/platforms/platform_stm32.h
@@ -34,7 +34,7 @@
 #include <stm32_sdk_hal.h>
 
 #define to64(x) strtoll(x, NULL, 10)
-#define INT64_FMT PRId64
+#define INT64_FMT "lld"
 #define SIZE_T_FMT "u"
 typedef struct stat cs_stat_t;
 #define DIRSEP '/'