diff --git a/target-s390x/helper.c b/target-s390x/helper.c
index 3180b90ed8..95f1ff5443 100644
--- a/target-s390x/helper.c
+++ b/target-s390x/helper.c
@@ -617,7 +617,7 @@ static void do_ext_interrupt(CPUS390XState *env)
 
 static void do_io_interrupt(CPUS390XState *env)
 {
-    uint64_t mask, addr;
+    uint64_t mask = 0, addr = 0;
     LowCore *lowcore;
     IOIntQueue *q;
     uint8_t isc;