diff --git a/inc/gcscandefs.h b/inc/gcscandefs.h
index af25b2f..5168651 100644
--- a/inc/gcscandefs.h
+++ b/inc/gcscandefs.h
@@ -1,6 +1,5 @@
 #ifndef GCSCANDEFS_H
 #define GCSCANDEFS_H 1
-#include "lispemul.h" /* for DLword */
-DLword gcscan1(int probe);
-DLword gcscan2(int probe);
+int gcscan1(int probe);
+int gcscan2(int probe);
 #endif
diff --git a/inc/inlineC.h b/inc/inlineC.h
index bd3cdf7..0e6822e 100644
--- a/inc/inlineC.h
+++ b/inc/inlineC.h
@@ -449,15 +449,15 @@
 
 #define GCSCAN1                                    \
   do {                                             \
-    TOPOFSTACK = gcscan1(TOPOFSTACK & 0xffff);     \
-    if (TOPOFSTACK) { TOPOFSTACK |= S_POSITIVE; }; \
+    int scan = gcscan1(TOPOFSTACK & 0xffff);     \
+    TOPOFSTACK = (scan == -1) ? NIL : (S_POSITIVE | scan); \
     nextop1;                                       \
   } while (0)
 
 #define GCSCAN2                                    \
   do {                                             \
-    TOPOFSTACK = gcscan2(TOPOFSTACK & 0xffff);     \
-    if (TOPOFSTACK) { TOPOFSTACK |= S_POSITIVE; }; \
+    int scan = gcscan2(TOPOFSTACK & 0xffff);     \
+    TOPOFSTACK = (scan == -1) ? NIL : (S_POSITIVE | scan); \
     nextop1;                                       \
   } while (0)
 
diff --git a/src/gc2.c b/src/gc2.c
index 074ab72..80481ef 100644
--- a/src/gc2.c
+++ b/src/gc2.c
@@ -40,13 +40,17 @@
 /**********************************************************************/
 
 void OP_gcscan1(void) {
-
+  int scan;
 #ifdef TRACE
   printPC();
   printf("TRACE: OP_gcscan1()\n");
 #endif
-  if ((TopOfStack & SEGMASK) == S_POSITIVE) { TopOfStack = gcscan1(LOLOC(TopOfStack)); }
-  if (TopOfStack != NIL) TopOfStack |= S_POSITIVE;
+  if ((TopOfStack & SEGMASK) == S_POSITIVE) {
+    scan = gcscan1(LOLOC(TopOfStack));
+    TopOfStack = (scan == -1) ? NIL : scan | S_POSITIVE;
+  } else {
+    printf("OP_gcscan1: not a number\n");
+  }
   PC++;
 } /* OP_gcscan1 end */
 
@@ -57,12 +61,14 @@ void OP_gcscan1(void) {
 /**********************************************************************/
 
 void OP_gcscan2(void) {
-
+  int scan;
 #ifdef TRACE
   printPC();
   printf("TRACE: OP_gcscan2()\n");
 #endif
-  if ((TopOfStack & SEGMASK) == S_POSITIVE) { TopOfStack = gcscan2(LOLOC(TopOfStack)); }
-  if (TopOfStack != NIL) TopOfStack |= S_POSITIVE;
+  if ((TopOfStack & SEGMASK) == S_POSITIVE) {
+    scan = gcscan2(LOLOC(TopOfStack));
+    TopOfStack = (scan == -1) ? NIL : scan | S_POSITIVE;
+  }
   PC++;
 } /* OP_gcscan2 end */
diff --git a/src/gcmain3.c b/src/gcmain3.c
index b50ebd8..f79f942 100644
--- a/src/gcmain3.c
+++ b/src/gcmain3.c
@@ -89,14 +89,14 @@
 
 
 LispPTR gcmapscan(void) {
-  GCENTRY probe;
+  int probe;
   GCENTRY *entry;
   GCENTRY offset, dbgcontents;
   LispPTR ptr;
 
   probe = HTMAIN_ENTRY_COUNT;
 nextentry:
-  while ((probe = gcscan1(probe)) != NIL) {
+  while ((probe = gcscan1(probe)) != -1) {
     entry = (GCENTRY *)HTmain + probe;
   retry:
     if (HENTRY->collision) {
@@ -135,12 +135,12 @@ nextentry:
 }
 
 LispPTR gcmapunscan(void) {
-  GCENTRY probe;
+  int probe;
   GCENTRY *entry;
   GCENTRY offset;
 
   probe = HTMAIN_ENTRY_COUNT;
-  while ((probe = gcscan2(probe)) != NIL) {
+  while ((probe = gcscan2(probe)) != -1) {
     entry = (GCENTRY *)HTmain + probe;
   retry:
     if (HENTRY->collision) {
diff --git a/src/gcscan.c b/src/gcscan.c
index bc426c7..16efc63 100644
--- a/src/gcscan.c
+++ b/src/gcscan.c
@@ -63,7 +63,7 @@
 #define GetStkCnt(entry1) (entry1 >> 9)
 #endif /* BIGVM */
 
-DLword gcscan1(int probe)
+int gcscan1(int probe)
 /* probe is offset */
 {
   struct htlinkptr *htlptr; /* overlay access method */
@@ -76,10 +76,10 @@ DLword gcscan1(int probe)
     if (contents && (((struct hashentry *)GCPTR(HTENDS))->collision || (GetStkCnt(contents) == 0)))
       return (probe);
   }
-  return (NIL);
+  return (-1);
 }
 
-DLword gcscan2(int probe)
+int gcscan2(int probe)
 /* probe is offset */
 {
   struct htlinkptr *htlptr; /* overlay access method */
@@ -90,5 +90,5 @@ DLword gcscan2(int probe)
     if (((HTSTKBIT | 1) & ((struct htlinkptr *)GCPTR(htlptr))->contents) != 0)
       return (probe); /* stackref or collision ON */
   }
-  return (NIL);
+  return (-1);
 }