diff --git a/gc.c b/gc.c
index 54643207..17a8126f 100644
--- a/gc.c
+++ b/gc.c
@@ -105,8 +105,15 @@ void sexp_conservative_mark (sexp ctx) {
         p = (sexp) (((char*)p) + r->size);
         continue;
       }
-      if (! sexp_gc_mark(p) && stack_references_pointer_p(ctx, p))
+      if (! sexp_gc_mark(p) && stack_references_pointer_p(ctx, p)) {
+#if SEXP_USE_DEBUG_GC > 1
+        if (p && sexp_pointerp(p)) {
+          fprintf(stderr, "GC MISS: %p: %s\n", p, sexp_pointer_source(p));
+          fflush(stderr);
+        }
+#endif
         sexp_mark(ctx, p);
+      }
       p = (sexp) (((char*)p)+sexp_heap_align(sexp_allocated_bytes(ctx, p)));
     }
   }
@@ -235,6 +242,9 @@ sexp sexp_gc (sexp ctx, size_t *sum_freed) {
   sexp_mark(ctx, ctx);
   sexp_conservative_mark(ctx);
 #if SEXP_USE_DEBUG_GC
+  fprintf(stderr, "******************** GC ********************\n");
+#endif
+#if SEXP_USE_DEBUG_GC > 2
   sexp_sweep_stats(ctx, 2, NULL, "* \x1B[31mFREE:\x1B[0m ");
 #endif
 #if SEXP_USE_WEAK_REFERENCES
diff --git a/include/chibi/features.h b/include/chibi/features.h
index a1c6d1cb..02e42ddf 100644
--- a/include/chibi/features.h
+++ b/include/chibi/features.h
@@ -77,6 +77,9 @@
 /* uncomment this to add additional native checks to only mark objects in the heap */
 /* #define SEXP_USE_SAFE_GC_MARK 1 */
 
+/* uncomment this to track what C source line each object is allocated from */
+/* #define SEXP_USE_TRACK_ALLOC_SOURCE 1 */
+
 /* uncomment this to add additional native gc checks to verify a magic header */
 /* #define SEXP_USE_HEADER_MAGIC 1 */
 
@@ -91,7 +94,7 @@
 /* uncomment this to make type definitions common to all contexts */
 /*   By default types are only global if you don't allow user type */
 /*   definitions, so new types will be local to a given set of */
-/*   contexts sharing thei heap. */
+/*   contexts sharing their heap. */
 /* #define SEXP_USE_GLOBAL_TYPES 1 */
 
 /* uncomment this to make the symbol table common to all contexts */
@@ -303,7 +306,11 @@
 #endif
 
 #ifndef SEXP_USE_CONSERVATIVE_GC
-#define SEXP_USE_CONSERVATIVE_GC 0
+#define SEXP_USE_CONSERVATIVE_GC SEXP_USE_DEBUG_GC > 1
+#endif
+
+#ifndef SEXP_USE_TRACK_ALLOC_SOURCE
+#define SEXP_USE_TRACK_ALLOC_SOURCE SEXP_USE_DEBUG_GC > 1
 #endif
 
 #ifndef SEXP_USE_HEADER_MAGIC
diff --git a/include/chibi/sexp.h b/include/chibi/sexp.h
index 3a2c75cb..16a23a4e 100644
--- a/include/chibi/sexp.h
+++ b/include/chibi/sexp.h
@@ -232,6 +232,9 @@ struct sexp_struct {
   unsigned int freep:1;
   unsigned int brokenp:1;
   unsigned int syntacticp:1;
+#if SEXP_USE_TRACK_ALLOC_SOURCE
+  const char* source;
+#endif
 #if SEXP_USE_HEADER_MAGIC
   unsigned int magic;
 #endif
@@ -444,13 +447,19 @@ void *sexp_realloc(sexp ctx, sexp x, size_t size);
 
 #define sexp_sizeof(x) (offsetof(struct sexp_struct, value) \
                          + sizeof(((sexp)0)->value.x))
-
 #define sexp_offsetof(type, f) (offsetof(struct sexp_struct, value.type.f))
-
 #define sexp_offsetof_slot0 (offsetof(struct sexp_struct, value))
-
 #define sexp_sizeof_header (sexp_sizeof(flonum) - sizeof(double))
 
+#if SEXP_USE_TRACK_ALLOC_SOURCE
+#define sexp_with_current_source0(file, line) file ": " #line
+#define sexp_with_current_source(file, line) , sexp_with_current_source0(file, line)
+#else
+#define sexp_with_current_source(file, line)
+#endif
+
+#define sexp_alloc_tagged(ctx, type, tag) sexp_alloc_tagged_aux(ctx, type, tag sexp_with_current_source(__FILE__, __LINE__))
+
 #define sexp_alloc_type(ctx, type, tag) sexp_alloc_tagged(ctx, sexp_sizeof(type), tag)
 #define sexp_alloc_bytecode(ctx, i) sexp_alloc_tagged(ctx, sexp_sizeof(bytecode) + i, SEXP_BYTECODE)
 
@@ -478,6 +487,12 @@ void *sexp_realloc(sexp ctx, sexp x, size_t size);
 #define sexp_brokenp(x)          ((x)->brokenp)
 #define sexp_pointer_magic(x)    ((x)->magic)
 
+#if SEXP_USE_TRACK_ALLOC_SOURCE
+#define sexp_pointer_source(x)   ((x)->source)
+#else
+#define sexp_pointer_source(x)   ""
+#endif
+
 #define sexp_check_tag(x,t)  (sexp_pointerp(x) && (sexp_pointer_tag(x) == (t)))
 
 #define sexp_slot_ref(x,i)   (((sexp*)&((x)->value))[i])
@@ -990,8 +1005,14 @@ SEXP_API sexp sexp_buffered_flush (sexp ctx, sexp p);
 #define sexp_at_eofp(p)      (feof(sexp_port_stream(p)))
 #define sexp_port_fileno(p)  (fileno(sexp_port_stream(p)))
 
+#if SEXP_USE_TRACK_ALLOC_SOURCE
+#define sexp_current_source_param , const char* source
+#else
+#define sexp_current_source_param
+#endif
+
+SEXP_API sexp sexp_alloc_tagged_aux(sexp ctx, size_t size, sexp_uint_t tag sexp_current_source_param);
 SEXP_API sexp sexp_make_context(sexp ctx, size_t size);
-SEXP_API sexp sexp_alloc_tagged(sexp ctx, size_t size, sexp_uint_t tag);
 SEXP_API sexp sexp_cons_op(sexp ctx sexp_api_params(self, n), sexp head, sexp tail);
 SEXP_API sexp sexp_list2(sexp ctx, sexp a, sexp b);
 SEXP_API sexp sexp_equalp_op (sexp ctx sexp_api_params(self, n), sexp a, sexp b);
diff --git a/sexp.c b/sexp.c
index db994d69..58700e80 100644
--- a/sexp.c
+++ b/sexp.c
@@ -47,10 +47,13 @@ static int is_separator(int c) {
 sexp sexp_symbol_table[SEXP_SYMBOL_TABLE_SIZE];
 #endif
 
-sexp sexp_alloc_tagged(sexp ctx, size_t size, sexp_uint_t tag) {
+sexp sexp_alloc_tagged_aux(sexp ctx, size_t size, sexp_uint_t tag sexp_current_source_param) {
   sexp res = (sexp) sexp_alloc(ctx, size);
   if (res && ! sexp_exceptionp(res)) {
     sexp_pointer_tag(res) = tag;
+#if SEXP_USE_TRACK_ALLOC_SOURCE
+    sexp_pointer_source(res) = source;
+#endif
 #if SEXP_USE_HEADER_MAGIC
     sexp_pointer_magic(res) = SEXP_POINTER_MAGIC;
 #endif