diff --git a/mythtv/libs/libmythtv/recorders/dvbcam.cpp b/mythtv/libs/libmythtv/recorders/dvbcam.cpp
index 4d0dd26b2fd..7bd1d3682c9 100644
--- a/mythtv/libs/libmythtv/recorders/dvbcam.cpp
+++ b/mythtv/libs/libmythtv/recorders/dvbcam.cpp
@@ -72,8 +72,12 @@ DVBCam::DVBCam(const QString &aDevice)
     if (cafd >= 0)
     {
         ca_caps_t caps;
-        ioctl(cafd, CA_GET_CAP, &caps);
-        numslots = caps.slot_num;
+        // slot_num will be uninitialised if ioctl fails
+        if (ioctl(cafd, CA_GET_CAP, &caps) >= 0)
+            numslots = caps.slot_num;
+        else
+            LOG(VB_GENERAL, LOG_ERR, "ioctl CA_GET_CAP failed");
+
         close(cafd);
     }
 }