diff --git a/libraries/SD/src/SD.cpp b/libraries/SD/src/SD.cpp
index f92532ca..40d16c86 100644
--- a/libraries/SD/src/SD.cpp
+++ b/libraries/SD/src/SD.cpp
@@ -80,7 +80,7 @@ uint64_t SDFS::totalBytes()
 	FATFS* fsinfo;
 	DWORD fre_clust;
 	if(f_getfree("0:",&fre_clust,&fsinfo)!= 0) return 0;
-    uint64_t size = (fsinfo->csize)*(fsinfo->n_fatent - 2)
+    uint64_t size = ((uint64_t)(fsinfo->csize))*(fsinfo->n_fatent - 2)
 #if _MAX_SS != 512
         *(fsinfo->ssize);
 #else
@@ -94,7 +94,7 @@ uint64_t SDFS::usedBytes()
 	FATFS* fsinfo;
 	DWORD fre_clust;
 	if(f_getfree("0:",&fre_clust,&fsinfo)!= 0) return 0;
-	uint64_t size = (fsinfo->csize)*((fsinfo->n_fatent - 2) - (fsinfo->free_clst))
+	uint64_t size = ((uint64_t)(fsinfo->csize))*((fsinfo->n_fatent - 2) - (fsinfo->free_clst))
 #if _MAX_SS != 512
         *(fsinfo->ssize);
 #else
diff --git a/libraries/SD_MMC/src/SD_MMC.cpp b/libraries/SD_MMC/src/SD_MMC.cpp
index d554413b..10476969 100644
--- a/libraries/SD_MMC/src/SD_MMC.cpp
+++ b/libraries/SD_MMC/src/SD_MMC.cpp
@@ -104,7 +104,7 @@ uint64_t SDMMCFS::totalBytes()
 	FATFS* fsinfo;
 	DWORD fre_clust;
 	if(f_getfree("0:",&fre_clust,&fsinfo)!= 0) return 0;
-    uint64_t size = (fsinfo->csize)*(fsinfo->n_fatent - 2)
+    uint64_t size = ((uint64_t)(fsinfo->csize))*(fsinfo->n_fatent - 2)
 #if _MAX_SS != 512
         *(fsinfo->ssize);
 #else
@@ -118,7 +118,7 @@ uint64_t SDMMCFS::usedBytes()
 	FATFS* fsinfo;
 	DWORD fre_clust;
 	if(f_getfree("0:",&fre_clust,&fsinfo)!= 0) return 0;
-	uint64_t size = (fsinfo->csize)*((fsinfo->n_fatent - 2) - (fsinfo->free_clst))
+	uint64_t size = ((uint64_t)(fsinfo->csize))*((fsinfo->n_fatent - 2) - (fsinfo->free_clst))
 #if _MAX_SS != 512
         *(fsinfo->ssize);
 #else