diff --git a/libguile/whippet/src/mmc.c b/libguile/whippet/src/mmc.c
index a65219a50..b35fd58b1 100644
--- a/libguile/whippet/src/mmc.c
+++ b/libguile/whippet/src/mmc.c
@@ -209,7 +209,8 @@ gc_visit_ephemeron_key(struct gc_edge edge, struct gc_heap *heap) {
   if (large_object_space_contains_with_lock(lospace, ref))
     return large_object_space_is_marked(lospace, ref);
 
-  GC_CRASH();
+  // Assume it is in the extern space.
+  return 1;
 }
 
 static int
@@ -585,9 +586,11 @@ grow_heap_if_necessary(struct gc_heap *heap,
   struct nofl_space *nofl = heap_nofl_space(heap);
   size_t pending = nofl_space_shrink(nofl, 0);
 
+  // If we cannot defragment and are making no progress but have a
+  // growable heap, expand by 25% to add some headroom.
   size_t needed_headroom =
     GC_CONSERVATIVE_TRACE
-    ? nofl_active_block_count (nofl) * NOFL_BLOCK_SIZE / 16
+    ? (progress ? 0 : nofl_active_block_count (nofl) * NOFL_BLOCK_SIZE / 4)
     : 0;
   size_t headroom = nofl_empty_block_count(nofl) * NOFL_BLOCK_SIZE;
 
diff --git a/libguile/whippet/src/pcc.c b/libguile/whippet/src/pcc.c
index f57b53b6c..d5eb50cd1 100644
--- a/libguile/whippet/src/pcc.c
+++ b/libguile/whippet/src/pcc.c
@@ -461,7 +461,9 @@ int gc_visit_ephemeron_key(struct gc_edge edge, struct gc_heap *heap) {
 
   if (large_object_space_contains_with_lock(heap_large_object_space(heap), ref))
     return large_object_space_is_marked(heap_large_object_space(heap), ref);
-  GC_CRASH();
+
+  // Assume it is in the extern space.
+  return 1;
 }
 
 static int mutators_are_stopping(struct gc_heap *heap) {
diff --git a/libguile/whippet/src/semi.c b/libguile/whippet/src/semi.c
index 9eaa6530d..d449dfc94 100644
--- a/libguile/whippet/src/semi.c
+++ b/libguile/whippet/src/semi.c
@@ -278,7 +278,8 @@ int gc_visit_ephemeron_key(struct gc_edge edge, struct gc_heap *heap) {
   } else if (large_object_space_contains_with_lock(heap_large_object_space(heap), ref)) {
     return large_object_space_is_marked(heap_large_object_space(heap), ref);
   }
-  GC_CRASH();
+  // Assume it is in the extern space.
+  return 1;
 }
 
 static void trace(struct gc_edge edge, struct gc_heap *heap, void *visit_data) {