diff --git a/driver.c b/driver.c
index f369b3a..b0aac6f 100644
--- a/driver.c
+++ b/driver.c
@@ -295,6 +295,7 @@ static Word DoMountURL(struct GSOSDP *dp) {
     //TODO report disk switch
     
     mountURLRec->result = OPERATION_SUCCESSFUL;
+    mountURLRec->devNum = dp->dibPointer->DIBDevNum;
     return 0;
 }
 
diff --git a/mounturl.h b/mounturl.h
index 439c613..96009ef 100644
--- a/mounturl.h
+++ b/mounturl.h
@@ -12,6 +12,7 @@ struct MountURLRec {
     Word byteCount;
     enum NetDiskError result; /* output value */
     char *url; /* C-string; will be modified */
+    Word devNum; /* output value: device number */
 };
 
 #endif