diff --git a/src/util/virbitmap.c b/src/util/virbitmap.c
index 3573b973ec..91df4b8601 100644
--- a/src/util/virbitmap.c
+++ b/src/util/virbitmap.c
@@ -825,11 +825,15 @@ virBitmapToDataBuf(virBitmapPtr bitmap,
                    unsigned char *bytes,
                    size_t len)
 {
+    size_t nbytes = bitmap->map_len * (VIR_BITMAP_BITS_PER_UNIT / CHAR_BIT);
     unsigned long *l;
     size_t i, j;
 
     memset(bytes, 0, len);
 
+    /* If bitmap and buffer differ in size, only fill to the smaller length */
+    len = MIN(len, nbytes);
+
     /* htole64 is not provided by gnulib, so we do the conversion by hand */
     l = bitmap->map;
     for (i = j = 0; i < len; i++, j++) {