diff --git a/sim_imd.c b/sim_imd.c
index 546b77de..ebaf64f1 100644
--- a/sim_imd.c
+++ b/sim_imd.c
@@ -1,6 +1,6 @@
 /*************************************************************************
  *                                                                       *
- * Copyright (c) 2007-2020 Howard M. Harte.                              *
+ * Copyright (c) 2007-2022 Howard M. Harte.                              *
  * https://github.com/hharte                                             *
  *                                                                       *
  * Permission is hereby granted, free of charge, to any person obtaining *
@@ -150,7 +150,10 @@ static t_stat diskParse(DISK_INFO *myDisk, uint32 isVerbose)
     do {
         sim_debug(myDisk->debugmask, myDisk->device, "start of track %d at file offset %ld\n", myDisk->ntracks, ftell(myDisk->file));
 
-        sim_fread(&imd, 1, 5, myDisk->file);
+        if (sim_fread(&imd, 1, 5, myDisk->file) != 5) {
+            return (SCPE_OPENERR);
+        }
+
         if (feof(myDisk->file))
             break;
         sectorSize = 128 << (imd.sectsize & 0x1f);
@@ -169,6 +172,18 @@ static t_stat diskParse(DISK_INFO *myDisk, uint32 isVerbose)
             myDisk->nsides = imd.head + 1;
         }
 
+        if (imd.head >= MAX_HEAD) {
+            sim_printf("SIM_IMD: Invalid head %d, a maximum of %d heads are supported.\n",
+                imd.head, MAX_HEAD);
+            return (SCPE_IERR);
+        }
+
+        if (imd.cyl >= MAX_CYL) {
+            sim_printf("SIM_IMD: Invalid cylinder %d, a maximum of %d cylinders are supported.\n",
+                imd.cyl, MAX_CYL);
+            return (SCPE_IERR);
+        }
+
         myDisk->track[imd.cyl][imd.head].mode = imd.mode;
         myDisk->track[imd.cyl][imd.head].nsects = imd.nsects;
         myDisk->track[imd.cyl][imd.head].sectsize = sectorSize;