diff --git a/src/duk_features.h.in b/src/duk_features.h.in
index 0e7a9917..2c744ebc 100644
--- a/src/duk_features.h.in
+++ b/src/duk_features.h.in
@@ -2521,16 +2521,20 @@ typedef FILE duk_file;
  */
 
 #undef DUK_USE_HSTRING_EXTDATA
-#undef DUK_USE_EXTSTR_INTERN_CHECK
-
 #if defined(DUK_OPT_EXTERNAL_STRINGS)
 #define DUK_USE_HSTRING_EXTDATA
 #endif
 
+#undef DUK_USE_EXTSTR_INTERN_CHECK
 #if defined(DUK_OPT_EXTERNAL_STRINGS) && defined(DUK_OPT_EXTSTR_INTERN_CHECK)
 #define DUK_USE_EXTSTR_INTERN_CHECK(ptr,len) DUK_OPT_EXTSTR_INTERN_CHECK((ptr), (len))
 #endif
 
+#undef DUK_USE_EXTSTR_FREE
+#if defined(DUK_OPT_EXTERNAL_STRINGS) && defined(DUK_OPT_EXTSTR_FREE)
+#define DUK_USE_EXTSTR_FREE(ptr) DUK_OPT_EXTSTR_FREE((ptr))
+#endif
+
 /*
  *  Lightweight functions
  */
diff --git a/src/duk_heap.h b/src/duk_heap.h
index 1ff55e67..38355715 100644
--- a/src/duk_heap.h
+++ b/src/duk_heap.h
@@ -402,6 +402,9 @@ duk_heap *duk_heap_alloc(duk_alloc_function alloc_func,
                          void *alloc_udata,
                          duk_fatal_function fatal_func);
 DUK_INTERNAL_DECL void duk_heap_free(duk_heap *heap);
+DUK_INTERNAL_DECL void duk_free_hobject_inner(duk_heap *heap, duk_hobject *h);
+DUK_INTERNAL_DECL void duk_free_hbuffer_inner(duk_heap *heap, duk_hbuffer *h);
+DUK_INTERNAL_DECL void duk_free_hstring_inner(duk_heap *heap, duk_hstring *h);
 DUK_INTERNAL_DECL void duk_heap_free_heaphdr_raw(duk_heap *heap, duk_heaphdr *hdr);
 
 DUK_INTERNAL_DECL void duk_heap_insert_into_heap_allocated(duk_heap *heap, duk_heaphdr *hdr);
diff --git a/src/duk_heap_alloc.c b/src/duk_heap_alloc.c
index 9eb1369b..db35ed0f 100644
--- a/src/duk_heap_alloc.c
+++ b/src/duk_heap_alloc.c
@@ -21,7 +21,7 @@
  *  been already dealt with.
  */
 
-DUK_LOCAL void duk__free_hobject_inner(duk_heap *heap, duk_hobject *h) {
+DUK_INTERNAL void duk_free_hobject_inner(duk_heap *heap, duk_hobject *h) {
 	DUK_ASSERT(heap != NULL);
 	DUK_ASSERT(h != NULL);
 
@@ -52,7 +52,7 @@ DUK_LOCAL void duk__free_hobject_inner(duk_heap *heap, duk_hobject *h) {
 	}
 }
 
-DUK_LOCAL void duk__free_hbuffer_inner(duk_heap *heap, duk_hbuffer *h) {
+DUK_INTERNAL void duk_free_hbuffer_inner(duk_heap *heap, duk_hbuffer *h) {
 	DUK_ASSERT(heap != NULL);
 	DUK_ASSERT(h != NULL);
 
@@ -63,6 +63,22 @@ DUK_LOCAL void duk__free_hbuffer_inner(duk_heap *heap, duk_hbuffer *h) {
 	}
 }
 
+DUK_INTERNAL void duk_free_hstring_inner(duk_heap *heap, duk_hstring *h) {
+	DUK_ASSERT(heap != NULL);
+	DUK_ASSERT(h != NULL);
+
+	DUK_UNREF(heap);
+	DUK_UNREF(h);
+
+#if defined(DUK_USE_HSTRING_EXTDATA) && defined(DUK_USE_EXTSTR_FREE)
+	if (DUK_HSTRING_HAS_EXTDATA(h)) {
+		DUK_DDD(DUK_DDDPRINT("free extstr: hstring %!O, extdata: %p",
+		                     h, DUK_HSTRING_GET_EXTDATA((duk_hstring_external *) h)));
+		DUK_USE_EXTSTR_FREE((const void *) DUK_HSTRING_GET_EXTDATA((duk_hstring_external *) h));
+	}
+#endif
+}
+
 DUK_INTERNAL void duk_heap_free_heaphdr_raw(duk_heap *heap, duk_heaphdr *hdr) {
 	DUK_ASSERT(heap);
 	DUK_ASSERT(hdr);
@@ -71,13 +87,13 @@ DUK_INTERNAL void duk_heap_free_heaphdr_raw(duk_heap *heap, duk_heaphdr *hdr) {
 
 	switch ((int) DUK_HEAPHDR_GET_TYPE(hdr)) {
 	case DUK_HTYPE_STRING:
-		/* no inner refs to free */
+		duk_free_hstring_inner(heap, (duk_hstring *) hdr);
 		break;
 	case DUK_HTYPE_OBJECT:
-		duk__free_hobject_inner(heap, (duk_hobject *) hdr);
+		duk_free_hobject_inner(heap, (duk_hobject *) hdr);
 		break;
 	case DUK_HTYPE_BUFFER:
-		duk__free_hbuffer_inner(heap, (duk_hbuffer *) hdr);
+		duk_free_hbuffer_inner(heap, (duk_hbuffer *) hdr);
 		break;
 	default:
 		DUK_UNREACHABLE();
@@ -165,11 +181,14 @@ DUK_LOCAL void duk__free_stringtable(duk_heap *heap) {
 #else
 			e = heap->strtable[i];
 #endif
-			if (e == DUK_STRTAB_DELETED_MARKER(heap)) {
+			if (e == NULL || e == DUK_STRTAB_DELETED_MARKER(heap)) {
 				continue;
 			}
+			DUK_ASSERT(e != NULL);
+
+			/* strings may have inner refs (extdata) in some cases */
+			duk_free_hstring_inner(heap, (duk_hstring *) e);
 
-			/* strings have no inner allocations so free directly */
 			DUK_DDD(DUK_DDDPRINT("FINALFREE (string): %!iO",
 			                     (duk_heaphdr *) e));
 			DUK_FREE(heap, e);
diff --git a/src/duk_heap_markandsweep.c b/src/duk_heap_markandsweep.c
index f05ef19a..b8c9efeb 100644
--- a/src/duk_heap_markandsweep.c
+++ b/src/duk_heap_markandsweep.c
@@ -558,12 +558,13 @@ DUK_LOCAL void duk__sweep_stringtable(duk_heap *heap, duk_size_t *out_count_keep
 		heap->strtable[i] = DUK_STRTAB_DELETED_MARKER(heap);
 #endif
 
-		/* then free */
-#if 1
-		DUK_FREE(heap, (duk_heaphdr *) h);  /* no inner refs/allocs, just free directly */
-#else
-		duk_heap_free_heaphdr_raw(heap, (duk_heaphdr *) h);  /* this would be OK but unnecessary */
-#endif
+		/* free inner references (these exist e.g. when external
+		 * strings are enabled)
+		 */
+		duk_free_hstring_inner(heap, (duk_hstring *) h);
+
+		/* finally free the struct itself */
+		DUK_FREE(heap, (duk_heaphdr *) h);
 	}
 
 #ifdef DUK_USE_DEBUG
diff --git a/src/duk_hstring.h b/src/duk_hstring.h
index ce05704e..5d00f6f6 100644
--- a/src/duk_hstring.h
+++ b/src/duk_hstring.h
@@ -102,8 +102,11 @@
 #endif
 
 #if defined(DUK_USE_HSTRING_EXTDATA)
+#define DUK_HSTRING_GET_EXTDATA(x) \
+	((x)->extdata)
 #define DUK_HSTRING_GET_DATA(x) \
-	(DUK_HSTRING_HAS_EXTDATA((x)) ? ((duk_hstring_external *) (x))->extdata : ((const duk_uint8_t *) ((x) + 1)))
+	(DUK_HSTRING_HAS_EXTDATA((x)) ? \
+		DUK_HSTRING_GET_EXTDATA((duk_hstring_external *) (x)) : ((const duk_uint8_t *) ((x) + 1)))
 #else
 #define DUK_HSTRING_GET_DATA(x) \
 	((const duk_uint8_t *) ((x) + 1))