diff --git a/ext2sim/ext2sim.c b/ext2sim/ext2sim.c
index 33d276fa..5d9de91f 100644
--- a/ext2sim/ext2sim.c
+++ b/ext2sim/ext2sim.c
@@ -175,13 +175,13 @@ typedef struct _devMerge {
         Dev * dev;
         int       esFMIndex;
         const HierName *hierName;
-        struct _devMerge *next;
+        const struct _devMerge *next;
 } devMerge;
 
 #ifdef EXT2SIM_AUTO
-devMerge *devMergeList = NULL ;
+const devMerge *devMergeList = NULL;
 #else
-extern devMerge *devMergeList;
+extern const devMerge *devMergeList;
 #endif
 
 /* attributes controlling the Area/Perimeter extraction of fet terminals */
@@ -679,13 +679,13 @@ runexttosim:
 
     if (esMergeDevsA || esMergeDevsC)
     {
-	devMerge *p;
+	const devMerge *p;
 
 	EFVisitDevs(simmergeVisit, PTR2CD(NULL));
 	TxPrintf("Devices merged: %d\n", esDevsMerged);
 	esFMIndex = 0;
 	for (p = devMergeList; p != NULL; p = p->next)
-	    freeMagic(p);
+	    freeMagic((char *)p);
 	devMergeList = NULL;
     }
 
@@ -808,12 +808,12 @@ main(
     EFFlatBuild(inName, flatFlags);
 
     if (esMergeDevsA || esMergeDevsC) {
-	devMerge *p;
+	const devMerge *p;
 
 	EFVisitDevs(simmergeVisit, PTR2CD(NULL));
 	TxPrintf("Devices merged: %d\n", esDevsMerged);
 	esFMIndex = 0;
-	for (p = devMergeList; p != NULL; p = p->next) freeMagic(p);
+	for (p = devMergeList; p != NULL; p = p->next) freeMagic((char *)p);
     }
 
     EFVisitDevs(simdevVisit, PTR2CD(NULL));
@@ -1797,7 +1797,8 @@ simmergeVisit(
 	const EFNode *subnode, *snode, *dnode, *gnode;
 	int      pmode, l, w;
 	float	 m;
-	devMerge *fp, *cfp;
+	devMerge *fp;
+	const devMerge *cfp;
 	const HierName *hierName = hc->hc_hierName;
 
 	if (dev->dev_nterm < 2) {
@@ -1842,7 +1843,7 @@ simmergeVisit(
 		setDevMult(fp->esFMIndex, DEV_KILLED);
 		setDevMult(cfp->esFMIndex, m);
 		esDevsMerged++;
-		freeMagic(fp);
+		freeMagic((char *)fp);
 		return 0;
 	  }
 	}
diff --git a/ext2spice/ext2hier.c b/ext2spice/ext2hier.c
index 7f090516..681cd77d 100644
--- a/ext2spice/ext2hier.c
+++ b/ext2spice/ext2hier.c
@@ -1156,7 +1156,8 @@ spcdevHierMergeVisit(hc, dev, scale)
     DevTerm *gate, *source, *drain;
     EFNode *subnode, *snode, *dnode, *gnode;
     int pmode, l, w;
-    devMerge *fp, *cfp;
+    devMerge *fp;
+    const devMerge *cfp;
     float m;
 
     /* If no terminals, or only a gate, can't do much of anything */
@@ -1564,7 +1565,8 @@ devMergeHierVisit(hc, dev, scale)
     EFNode *subnode, *snode, *dnode, *gnode;
     int      pmode, l, w;
     bool     hS, hD, chS, chD;
-    devMerge *fp, *cfp;
+    devMerge *fp;
+    const devMerge *cfp;
     float m;
 
     if (esDistrJunct)
@@ -2179,13 +2181,13 @@ esHierVisit(hc, cdata)
 	/* Merge devices */
 	if (esMergeDevsA || esMergeDevsC)
 	{
-	    devMerge *p;
+	    const devMerge *p;
 
 	    EFHierVisitDevs(hcf, spcdevHierMergeVisit, (ClientData)NULL);
 	    TxPrintf("Devs merged: %d\n", esSpiceDevsMerged);
 	    esFMIndex = 0;
 	    for (p = devMergeList; p != NULL; p = p->next)
-		freeMagic(p);
+		freeMagic((char *)p);
 	    devMergeList = NULL;
 	}
 	else if (esDistrJunct)
diff --git a/ext2spice/ext2spice.c b/ext2spice/ext2spice.c
index e12ae596..11d8c728 100644
--- a/ext2spice/ext2spice.c
+++ b/ext2spice/ext2spice.c
@@ -112,7 +112,7 @@ int	 esFMIndex = 0;          /* current index to it */
 int	 esFMSize = FMULT_SIZE ; /* its current size (growable) */
 int	 esSpiceDevsMerged;
 
-devMerge *devMergeList = NULL ;
+const devMerge *devMergeList = NULL ;
 
 #define        atoCap(s)       ((EFCapValue)atof(s))
 
@@ -1106,13 +1106,13 @@ runexttospice:
 
 	if (esMergeDevsA || esMergeDevsC)
 	{
-	    devMerge *p;
+	    const devMerge *p;
 
 	    EFVisitDevs(devMergeVisit, (ClientData) NULL);
 	    TxPrintf("Devs merged: %d\n", esSpiceDevsMerged);
 	    esFMIndex = 0;
 	    for (p = devMergeList; p != NULL; p = p->next)
-		freeMagic(p);
+		freeMagic((char *) p);
 	    devMergeList = NULL;
 	}
 	else if (esDistrJunct)
@@ -1287,9 +1287,9 @@ main(argc, argv)
 	TxPrintf("Devs merged: %d\n", esSpiceDevsMerged);
 	esFMIndex = 0 ;
 	{
-	  devMerge *p;
+	  const devMerge *p;
 
-	  for ( p = devMergeList ; p != NULL ; p=p->next ) freeMagic(p);
+	  for ( p = devMergeList ; p != NULL ; p=p->next ) freeMagic((char *)p);
 	}
     } else if ( esDistrJunct )
      	EFVisitDevs(devDistJunctVisit, (ClientData) NULL);
@@ -4291,7 +4291,8 @@ devMergeVisit(dev, hc, scale, trans)
     EFNode *subnode, *snode, *dnode, *gnode;
     int      pmode, l, w;
     bool     hS, hD, chS, chD;
-    devMerge *fp, *cfp;
+    devMerge *fp;
+    const devMerge *cfp;
     float m;
     HierName *hierName = hc->hc_hierName;
 
diff --git a/ext2spice/ext2spice.h b/ext2spice/ext2spice.h
index 7e813b7c..894724e9 100644
--- a/ext2spice/ext2spice.h
+++ b/ext2spice/ext2spice.h
@@ -13,7 +13,7 @@ typedef struct _devMerge {
 	Dev * dev;
 	int	  esFMIndex;
 	HierName *hierName;
-	struct _devMerge *next;
+	const struct _devMerge *next;
 } devMerge;
 
 /* Forward declarations */
@@ -89,7 +89,7 @@ extern int	 esFMIndex;     /* current index to it */
 extern int	 esFMSize; 	/* its current size (growable) */
 
 extern int	 esSpiceDevsMerged;
-extern devMerge *devMergeList;
+extern const devMerge *devMergeList;
 
 /*
  * The following hash table and associated functions are used only if