diff --git a/src/dos/dos_programs.cpp b/src/dos/dos_programs.cpp
index 4f0fad77..034e5605 100644
--- a/src/dos/dos_programs.cpp
+++ b/src/dos/dos_programs.cpp
@@ -1229,7 +1229,7 @@ public:
 					return;
 				}
 				int i_drive = toupper(temp_line[0]);
-				if (!isalpha(drive) || (i_drive - 'A') >= DOS_DRIVES || (i_drive - 'A') <0) {
+				if (!isalpha(i_drive) || (i_drive - 'A') >= DOS_DRIVES || (i_drive - 'A') <0) {
 					WriteOut_NoParsing(MSG_Get("PROGRAM_IMGMOUNT_SPECIFY_DRIVE"));
 					return;
 				}