diff --git a/VERSION b/VERSION
index 774046f..7defbbd 100644
--- a/VERSION
+++ b/VERSION
@@ -1 +1 @@
-1.5.261
+1.5.262
diff --git a/base/ext.c b/base/ext.c
index 55fdf7d..e0d2f86 100644
--- a/base/ext.c
+++ b/base/ext.c
@@ -462,11 +462,6 @@ void simCell(char *name, int filenum)
     return;
   }
 
-  /* Check procedure disabled because new extensions to .sim format
-   * allow 'x' records to represent low-level components that are
-   * modeled as SPICE subcircuits.
-   */
-#if 0
   /* check to see that all children have been dumped */
   ob = tp->cell;
   while (ob != NULL) {
@@ -478,7 +473,6 @@ void simCell(char *name, int filenum)
     }
     ob = ob->next;
   }
-#endif
 
   SetExtension(FileName, name, SIM_EXTENSION);
   if (!OpenFile(FileName, 0)) {
@@ -603,7 +597,7 @@ void simCell(char *name, int filenum)
 	    FlushString(" %g\n", v);   
 	    break;
 
-	 case CLASS_SUBCKT: case CLASS_MODULE:
+	 case CLASS_MODULE:
 	    *writeLine = 'x';
 	    *(writeLine + 1) = '\0';
 	    mult = 1;
@@ -812,7 +806,7 @@ char *ReadPrm(char *fname, int *fnum)
 	     PropertyDouble(devicename, filenum, "w", 0.01, 0.0);
 	     PropertyInteger(devicename, filenum, "nf", 0, 1);
 	     PropertyInteger(devicename, filenum, "m", 0, 1);
-	     SetClass(CLASS_SUBCKT);
+	     SetClass(CLASS_MODULE);
 	     EndCell();
 	     ReopenCellDef(fname, filenum);
 	 }
@@ -833,7 +827,7 @@ char *ReadPrm(char *fname, int *fnum)
 	     PropertyDouble(devicename, filenum, "w", 0.01, 0.0);
 	     PropertyInteger(devicename, filenum, "nf", 0, 1);
 	     PropertyInteger(devicename, filenum, "m", 0, 1);
-	     SetClass(CLASS_SUBCKT);
+	     SetClass(CLASS_MODULE);
 	     EndCell();
 	     ReopenCellDef(fname, filenum);
 	 }
@@ -855,7 +849,7 @@ char *ReadPrm(char *fname, int *fnum)
 	    PropertyDouble(devicename, filenum, "l", 0.01, 0.0);
 	    PropertyDouble(devicename, filenum, "w", 0.01, 0.0);
 	    PropertyInteger(devicename, filenum, "m", 0, 1);
-            SetClass(CLASS_SUBCKT);
+            SetClass(CLASS_MODULE);
             EndCell();
             ReopenCellDef(fname, filenum);
          }
@@ -877,7 +871,7 @@ char *ReadPrm(char *fname, int *fnum)
 	    PropertyDouble(devicename, filenum, "l", 0.01, 0.0);
 	    PropertyDouble(devicename, filenum, "w", 0.01, 0.0);
 	    PropertyInteger(devicename, filenum, "m", 0, 1);
-            SetClass(CLASS_SUBCKT);
+            SetClass(CLASS_MODULE);
             EndCell();
             ReopenCellDef(fname, filenum);  /* Reopen */
          }
@@ -893,7 +887,7 @@ char *ReadPrm(char *fname, int *fnum)
             Port("anode");
             Port("cathode");
 	    PropertyInteger(devicename, filenum, "m", 0, 1);
-            SetClass(CLASS_SUBCKT);
+            SetClass(CLASS_MODULE);
             EndCell();
             ReopenCellDef(fname, filenum);  /* Reopen */
          }
diff --git a/base/flatten.c b/base/flatten.c
index a42e03c..3742931 100644
--- a/base/flatten.c
+++ b/base/flatten.c
@@ -136,17 +136,16 @@ void flattenCell(char *name, int file)
 	    ob2 = ob2->next;
 	}
     
-
       /* delete all port elements from child */
       while (IsPort(ChildObjList)) {
 	/* delete all ports at beginning of list */
 	if (Debug) Printf("deleting leading port from child\n");
 	tmp = ChildObjList->next;
 	FreeObjectAndHash(ChildObjList, ChildCell);
-	ChildObjList = tmp;
+        if ((ChildObjList = tmp) == NULL) break;
       }
       tmp = ChildObjList;
-      while (tmp->next != NULL) {
+      while (tmp && (tmp->next != NULL)) {
 	if (IsPort(tmp->next)) {
 	  ob2 = (tmp->next)->next;
 	  if (Debug) Printf("deleting a port from child\n");
diff --git a/tcltk/netgen.tcl.in b/tcltk/netgen.tcl.in
index 7fff096..164850c 100644
--- a/tcltk/netgen.tcl.in
+++ b/tcltk/netgen.tcl.in
@@ -741,6 +741,19 @@ set auto_noexec 1       ;# don't EVER call UNIX commands w/o "shell" in front
 # Cross-Application section
 #----------------------------------------------------------------------
 
+# For use with open_pdks, set PDK_ROOT from the environment.  If no
+# such environment variable exists, check some common locations.
+
+if {[catch {set PDK_ROOT $::env(PDK_ROOT)}]} {
+    if {[file isdir /usr/local/share/pdk] == 1} {
+	set PDK_ROOT /usr/local/share/pdk
+    } elseif {[file isdir /usr/share/pdk] == 1} {
+	set PDK_ROOT /usr/share/pdk
+    } elseif {[file isdir /foss/pdk] == 1} {
+	set PDK_ROOT /foss/pdk
+    }
+}
+
 # Setup IRSIM assuming that the Tcl version is installed.
 # We do not need to rename procedure irsim to NULL because it is
 # redefined in a script, which simply overwrites the original.