diff --git a/target/s390x/ioinst.c b/target/s390x/ioinst.c
index 4eb0a7a9f8..bdae5090bc 100644
--- a/target/s390x/ioinst.c
+++ b/target/s390x/ioinst.c
@@ -123,7 +123,7 @@ static int ioinst_schib_valid(SCHIB *schib)
     }
     /* for MB format 1 bits 26-31 of word 11 must be 0 */
     /* MBA uses words 10 and 11, it means align on 2**6 */
-    if ((be16_to_cpu(schib->pmcw.chars) & PMCW_CHARS_MASK_MBFC) &&
+    if ((be32_to_cpu(schib->pmcw.chars) & PMCW_CHARS_MASK_MBFC) &&
         (be64_to_cpu(schib->mba) & 0x03fUL)) {
         return 0;
     }