diff --git a/env/fat.c b/env/fat.c
index b04b1d9c315..1ad301eaaff 100644
--- a/env/fat.c
+++ b/env/fat.c
@@ -41,14 +41,12 @@ __weak const char *env_fat_get_intf(void)
 __weak char *env_fat_get_dev_part(void)
 {
 #ifdef CONFIG_MMC
-	static char *part_str;
+	/* reserve one more char for the manipulation below */
+	static char part_str[] = CONFIG_ENV_FAT_DEVICE_AND_PART "\0";
 
-	if (!part_str) {
-		part_str = CONFIG_ENV_FAT_DEVICE_AND_PART;
-		if (!strcmp(CONFIG_ENV_FAT_INTERFACE, "mmc") && part_str[0] == ':') {
-			part_str = "0" CONFIG_ENV_FAT_DEVICE_AND_PART;
-			part_str[0] += mmc_get_env_dev();
-		}
+	if (!strcmp(CONFIG_ENV_FAT_INTERFACE, "mmc") && part_str[0] == ':') {
+		part_str[0] = '0' + mmc_get_env_dev();
+		strcpy(&part_str[1], CONFIG_ENV_FAT_DEVICE_AND_PART);
 	}
 
 	return part_str;