diff --git a/tools/mkenvimage.c b/tools/mkenvimage.c
index 716cb73a5c..8cd9ffa1c6 100644
--- a/tools/mkenvimage.c
+++ b/tools/mkenvimage.c
@@ -162,7 +162,7 @@ int main(int argc, char **argv)
 		txt_fd = STDIN_FILENO;
 
 		do {
-			filebuf = realloc(filebuf, readlen);
+			filebuf = realloc(filebuf, filesize + readlen);
 			if (!filebuf) {
 				fprintf(stderr, "Can't realloc memory for the input file buffer\n");
 				return EXIT_FAILURE;