diff --git a/extlib/benz/gc.c b/extlib/benz/gc.c
index 5c5ef412..0db0c4c1 100644
--- a/extlib/benz/gc.c
+++ b/extlib/benz/gc.c
@@ -530,6 +530,20 @@ gc_mark_trie(pic_state *pic, struct pic_trie *trie)
 static void
 gc_mark_global_symbols(pic_state *pic)
 {
+  M(sDEFINE); M(sLAMBDA); M(sIF); M(sBEGIN); M(sQUOTE); M(sSETBANG);
+  M(sQUASIQUOTE); M(sUNQUOTE); M(sUNQUOTE_SPLICING);
+  M(sDEFINE_SYNTAX); M(sIMPORT); M(sEXPORT);
+  M(sDEFINE_LIBRARY); M(sIN_LIBRARY);
+  M(sCOND_EXPAND); M(sAND); M(sOR); M(sELSE); M(sLIBRARY);
+  M(sONLY); M(sRENAME); M(sPREFIX); M(sEXCEPT);
+  M(sCONS); M(sCAR); M(sCDR); M(sNILP);
+  M(sSYMBOLP); M(sPAIRP);
+  M(sADD); M(sSUB); M(sMUL); M(sDIV); M(sMINUS);
+  M(sEQ); M(sLT); M(sLE); M(sGT); M(sGE); M(sNOT);
+  M(sREAD); M(sFILE);
+  M(sCALL); M(sTAILCALL); M(sCALL_WITH_VALUES); M(sTAILCALL_WITH_VALUES);
+  M(sGREF); M(sLREF); M(sCREF); M(sRETURN);
+
   M(rDEFINE); M(rLAMBDA); M(rIF); M(rBEGIN); M(rQUOTE); M(rSETBANG);
   M(rDEFINE_SYNTAX); M(rIMPORT); M(rEXPORT);
   M(rDEFINE_LIBRARY); M(rIN_LIBRARY);
@@ -573,14 +587,9 @@ gc_mark_phase(pic_state *pic)
     gc_mark_object(pic, pic->arena[j]);
   }
 
-  /* mark reserved uninterned symbols */
+  /* mark reserved symbols */
   gc_mark_global_symbols(pic);
 
-  /* mark all interned symbols */
-  for (it = xh_begin(&pic->syms); it != NULL; it = xh_next(it)) {
-    gc_mark_object(pic, (struct pic_object *)xh_val(it, pic_sym *));
-  }
-
   /* global variables */
   if (pic->globals) {
     gc_mark_object(pic, (struct pic_object *)pic->globals);
@@ -709,6 +718,31 @@ gc_finalize_object(pic_state *pic, struct pic_object *obj)
   }
 }
 
+static void
+gc_sweep_symbols(pic_state *pic)
+{
+  xh_entry *it;
+  xvect xv;
+  size_t i;
+  char *cstr;
+
+  xv_init(&xv, sizeof(xh_entry *));
+
+  for (it = xh_begin(&pic->syms); it != NULL; it = xh_next(it)) {
+    if (! gc_obj_is_marked((struct pic_object *)xh_val(it, pic_sym *))) {
+      xv_push(&xv, &it);
+    }
+  }
+
+  for (i = 0; i < xv_size(&xv); ++i) {
+    cstr = xh_key(*(xh_entry **)xv_get(&xv, i), char *);
+
+    xh_del_str(&pic->syms, cstr);
+
+    pic_free(pic, cstr);
+  }
+}
+
 static void
 gc_sweep_page(pic_state *pic, struct heap_page *page)
 {
@@ -775,6 +809,8 @@ gc_sweep_phase(pic_state *pic)
     }
   } while (it != NULL);
 
+  gc_sweep_symbols(pic);
+
   while (page) {
     gc_sweep_page(pic, page);
     page = page->next;