diff --git a/runtime.c b/runtime.c
index cdaaa0e..01f26df 100644
--- a/runtime.c
+++ b/runtime.c
@@ -3267,6 +3267,15 @@ C_regparm void C_fcall really_mark(C_word *x)
     if(is_fptr(h)) {
       val = fptr_to_ptr(h);
 
+      /* When we marked the bucket, it may have already referred
+       * to the _moved_ symbol. Re-check:
+       */
+      if(C_enable_gcweak &&
+         (C_block_header(val) & C_HEADER_TYPE_BITS) == C_SYMBOL_TYPE &&
+         (wep = lookup_weak_table_entry(*x, 0)) != NULL) {
+        if((wep->container & WEAK_COUNTER_MAX) == 0) ++wep->container;
+      }
+
       if((C_uword)val >= (C_uword)tospace_start && (C_uword)val < (C_uword)tospace_top) {
 	*x = val;
 	return;
@@ -3280,6 +3289,17 @@ C_regparm void C_fcall really_mark(C_word *x)
 	/* Link points into fromspace and into a link which points into from- or tospace: */
 	val = fptr_to_ptr(h);
 	
+        /* See above: might happen twice */
+        if(C_enable_gcweak &&
+           (C_block_header(val) & C_HEADER_TYPE_BITS) == C_SYMBOL_TYPE &&
+           ((wep = lookup_weak_table_entry((C_word)p, 0)) != NULL ||
+            /* Also check against original location if forwarded later.
+             * TODO: Can this even occur?
+             */
+            (wep = lookup_weak_table_entry(*x, 0)) != NULL)) {
+          if((wep->container & WEAK_COUNTER_MAX) == 0) ++wep->container;
+        }
+
 	if((C_uword)val >= (C_uword)tospace_start && (C_uword)val < (C_uword)tospace_top) {
 	  *x = val;
 	  return;