diff --git a/src/ccl.c b/src/ccl.c
index ec108e30d8..c853e61982 100644
--- a/src/ccl.c
+++ b/src/ccl.c
@@ -2062,7 +2062,7 @@ #define CCL_EXECUTE_BUF_SIZE 1024
       if (TYPE_RANGED_FIXNUMP (int, AREF (status, i)))
 	ccl.reg[i] = XFIXNUM (AREF (status, i));
     }
-  if (FIXNUMP (AREF (status, i)))
+  if (FIXNATP (AREF (status, i)))
     {
       i = XFIXNAT (AREF (status, 8));
       if (ccl.ic < i && i < ccl.size)
diff --git a/src/dosfns.c b/src/dosfns.c
index 47c545007a..fb5bcc9ad3 100644
--- a/src/dosfns.c
+++ b/src/dosfns.c
@@ -72,7 +72,7 @@ DEFUN ("int86", Fint86, Sint86, 2, 2, 0,
   if (no < 0 || no > 0xff || ASIZE (registers) != 8)
     return Qnil;
   for (i = 0; i < 8; i++)
-    CHECK_FIXNUM (AREF (registers, i));
+    CHECK_FIXNAT (AREF (registers, i));
 
   inregs.x.ax    = (unsigned long) XFIXNAT (AREF (registers, 0));
   inregs.x.bx    = (unsigned long) XFIXNAT (AREF (registers, 1));
@@ -139,7 +139,7 @@ DEFUN ("msdos-memput", Fdos_memput, Sdos_memput, 2, 2, 0,
 
   for (i = 0; i < len; i++)
     {
-      CHECK_FIXNUM (AREF (vector, i));
+      CHECK_FIXNAT (AREF (vector, i));
       buf[i] = (unsigned char) XFIXNAT (AREF (vector, i)) & 0xFF;
     }
 
diff --git a/src/fileio.c b/src/fileio.c
index 5dd14daacb..b2db6efd54 100644
--- a/src/fileio.c
+++ b/src/fileio.c
@@ -4719,7 +4719,7 @@ because (1) it preserves some marker positions and (2) it puts less data
 		 the format conversion.  */
 	      Lisp_Object tem = XCAR (old_undo);
 	      if (CONSP (tem) && FIXNUMP (XCAR (tem))
-		  && FIXNUMP (XCDR (tem))
+		  && FIXNATP (XCDR (tem))
 		  && XFIXNAT (XCDR (tem)) == PT + old_inserted)
 		XSETCDR (tem, make_fixnum (PT + inserted));
 	    }
@@ -5391,7 +5391,7 @@ a_write (int desc, Lisp_Object string, ptrdiff_t pos,
     {
       tem = Fcar_safe (Fcar (*annot));
       nextpos = pos - 1;
-      if (FIXNUMP (tem))
+      if (FIXNATP (tem))
 	nextpos = XFIXNAT (tem);
 
       /* If there are no more annotations in this range,
@@ -5847,7 +5847,7 @@ DEFUN ("do-auto-save", Fdo_auto_save, Sdo_auto_save, 0, 2, "",
 
 	    set_buffer_internal (b);
 	    if (NILP (Vauto_save_include_big_deletions)
-		&& FIXNUMP (BVAR (b, save_length))
+		&& FIXNATP (BVAR (b, save_length))
 		/* A short file is likely to change a large fraction;
 		   spare the user annoying messages.  */
 		&& XFIXNAT (BVAR (b, save_length)) > 5000
diff --git a/src/image.c b/src/image.c
index 7b648c46ae..2ecea0893f 100644
--- a/src/image.c
+++ b/src/image.c
@@ -2385,7 +2385,7 @@ lookup_image (struct frame *f, Lisp_Object spec)
 #endif
 
 	  ascent = image_spec_value (spec, QCascent, NULL);
-	  if (FIXNUMP (ascent))
+	  if (FIXNATP (ascent))
 	    img->ascent = XFIXNAT (ascent);
 	  else if (EQ (ascent, Qcenter))
 	    img->ascent = CENTERED_IMAGE_ASCENT;
diff --git a/src/lisp.h b/src/lisp.h
index 77fc22d118..a1bd6d8f6b 100644
--- a/src/lisp.h
+++ b/src/lisp.h
@@ -2968,6 +2968,14 @@ #define CHECK_FIXNUM_COERCE_MARKER(x)					\
       CHECK_TYPE (FIXNUMP (x), Qinteger_or_marker_p, x);		\
   } while (false)
 
+#define CHECK_FIXNAT_COERCE_MARKER(x)					\
+  do {									\
+    if (MARKERP ((x)))							\
+      XSETFASTINT (x, marker_position (x));				\
+    else								\
+      CHECK_TYPE (FIXNATP (x), Qinteger_or_marker_p, x);		\
+  } while (false)
+
 INLINE double
 XFLOATINT (Lisp_Object n)
 {
diff --git a/src/process.c b/src/process.c
index 6717ccb418..6bc3c75190 100644
--- a/src/process.c
+++ b/src/process.c
@@ -2673,7 +2673,7 @@ conv_lisp_to_sockaddr (int family, Lisp_Object address, struct sockaddr *sa, int
 	  hostport = XFIXNUM (p->contents[--len]);
 	  sin6->sin6_port = htons (hostport);
 	  for (i = 0; i < len; i++)
-	    if (FIXNUMP (p->contents[i]))
+	    if (FIXNATP (p->contents[i]))
 	      {
 		int j = XFIXNAT (p->contents[i]) & 0xffff;
 		ip6[i] = ntohs (j);
diff --git a/src/textprop.c b/src/textprop.c
index ae42c44185..6b20a34820 100644
--- a/src/textprop.c
+++ b/src/textprop.c
@@ -134,8 +134,8 @@ validate_interval_range (Lisp_Object object, Lisp_Object *begin,
   ptrdiff_t searchpos;
 
   CHECK_STRING_OR_BUFFER (object);
-  CHECK_FIXNUM_COERCE_MARKER (*begin);
-  CHECK_FIXNUM_COERCE_MARKER (*end);
+  CHECK_FIXNAT_COERCE_MARKER (*begin);
+  CHECK_FIXNAT_COERCE_MARKER (*end);
 
   /* If we are asked for a point, but from a subr which operates
      on a range, then return nothing.  */
@@ -790,14 +790,14 @@ DEFUN ("next-single-char-property-change", Fnext_single_char_property_change,
 	  Fset_buffer (object);
 	}
 
-      CHECK_FIXNUM_COERCE_MARKER (position);
+      CHECK_FIXNAT_COERCE_MARKER (position);
 
       initial_value = Fget_char_property (position, prop, object);
 
       if (NILP (limit))
 	XSETFASTINT (limit, ZV);
       else
-	CHECK_FIXNUM_COERCE_MARKER (limit);
+	CHECK_FIXNAT_COERCE_MARKER (limit);
 
       if (XFIXNAT (position) >= XFIXNAT (limit))
 	{
@@ -874,12 +874,12 @@ DEFUN ("previous-single-char-property-change",
 	  Fset_buffer (object);
 	}
 
-      CHECK_FIXNUM_COERCE_MARKER (position);
+      CHECK_FIXNAT_COERCE_MARKER (position);
 
       if (NILP (limit))
 	XSETFASTINT (limit, BEGV);
       else
-	CHECK_FIXNUM_COERCE_MARKER (limit);
+	CHECK_FIXNAT_COERCE_MARKER (limit);
 
       if (XFIXNAT (position) <= XFIXNAT (limit))
 	{
@@ -942,7 +942,7 @@ DEFUN ("next-property-change", Fnext_property_change,
     XSETBUFFER (object, current_buffer);
 
   if (!NILP (limit) && !EQ (limit, Qt))
-    CHECK_FIXNUM_COERCE_MARKER (limit);
+    CHECK_FIXNAT_COERCE_MARKER (limit);
 
   i = validate_interval_range (object, &position, &position, soft);
 
@@ -975,7 +975,7 @@ DEFUN ("next-property-change", Fnext_property_change,
 
   if (!next
       || (next->position
-	  >= (FIXNUMP (limit)
+	  >= (FIXNATP (limit)
 	      ? XFIXNAT (limit)
 	      : (STRINGP (object)
 		 ? SCHARS (object)
@@ -1009,7 +1009,7 @@ DEFUN ("next-single-property-change", Fnext_single_property_change,
     XSETBUFFER (object, current_buffer);
 
   if (!NILP (limit))
-    CHECK_FIXNUM_COERCE_MARKER (limit);
+    CHECK_FIXNAT_COERCE_MARKER (limit);
 
   i = validate_interval_range (object, &position, &position, soft);
   if (!i)
@@ -1024,7 +1024,7 @@ DEFUN ("next-single-property-change", Fnext_single_property_change,
 
   if (!next
       || (next->position
-	  >= (FIXNUMP (limit)
+	  >= (FIXNATP (limit)
 	      ? XFIXNAT (limit)
 	      : (STRINGP (object)
 		 ? SCHARS (object)
@@ -1056,7 +1056,7 @@ DEFUN ("previous-property-change", Fprevious_property_change,
     XSETBUFFER (object, current_buffer);
 
   if (!NILP (limit))
-    CHECK_FIXNUM_COERCE_MARKER (limit);
+    CHECK_FIXNAT_COERCE_MARKER (limit);
 
   i = validate_interval_range (object, &position, &position, soft);
   if (!i)
@@ -1074,7 +1074,7 @@ DEFUN ("previous-property-change", Fprevious_property_change,
 
   if (!previous
       || (previous->position + LENGTH (previous)
-	  <= (FIXNUMP (limit)
+	  <= (FIXNATP (limit)
 	      ? XFIXNAT (limit)
 	      : (STRINGP (object) ? 0 : BUF_BEGV (XBUFFER (object))))))
     return limit;
@@ -1106,7 +1106,7 @@ DEFUN ("previous-single-property-change", Fprevious_single_property_change,
     XSETBUFFER (object, current_buffer);
 
   if (!NILP (limit))
-    CHECK_FIXNUM_COERCE_MARKER (limit);
+    CHECK_FIXNAT_COERCE_MARKER (limit);
 
   i = validate_interval_range (object, &position, &position, soft);
 
@@ -1127,7 +1127,7 @@ DEFUN ("previous-single-property-change", Fprevious_single_property_change,
 
   if (!previous
       || (previous->position + LENGTH (previous)
-	  <= (FIXNUMP (limit)
+	  <= (FIXNATP (limit)
 	      ? XFIXNAT (limit)
 	      : (STRINGP (object) ? 0 : BUF_BEGV (XBUFFER (object))))))
     return limit;
@@ -1353,8 +1353,8 @@ set_text_properties (Lisp_Object start, Lisp_Object end, Lisp_Object properties,
   /* If we want no properties for a whole string,
      get rid of its intervals.  */
   if (NILP (properties) && STRINGP (object)
-      && XFIXNAT (start) == 0
-      && XFIXNAT (end) == SCHARS (object))
+      && FIXNATP (start) && XFIXNAT (start) == 0
+      && FIXNATP (end) && XFIXNAT (end) == SCHARS (object))
     {
       if (!string_intervals (object))
 	return Qnil;
diff --git a/src/w32term.c b/src/w32term.c
index 5726124b0e..886fc6c751 100644
--- a/src/w32term.c
+++ b/src/w32term.c
@@ -2463,7 +2463,7 @@ w32_draw_glyph_string (struct glyph_string *s)
 		  Lisp_Object val
 		    = buffer_local_value (Qunderline_minimum_offset,
 					s->w->contents);
-		  if (FIXNUMP (val))
+		  if (FIXNATP (val))
 		    minimum_offset = XFIXNAT (val);
 		  else
 		    minimum_offset = 1;
diff --git a/src/xterm.c b/src/xterm.c
index 1acff2af0d..64467e0d92 100644
--- a/src/xterm.c
+++ b/src/xterm.c
@@ -3806,7 +3806,7 @@ x_draw_glyph_string (struct glyph_string *s)
 		  Lisp_Object val
 		    = buffer_local_value (Qunderline_minimum_offset,
 					  s->w->contents);
-		  if (FIXNUMP (val))
+		  if (FIXNATP (val))
 		    minimum_offset = XFIXNAT (val);
 		  else
 		    minimum_offset = 1;