diff --git a/src/bitreader.c b/src/bitreader.c
index 0b406e0..d3553f0 100644
--- a/src/bitreader.c
+++ b/src/bitreader.c
@@ -13,14 +13,37 @@ long long read_bits(input_stream_t* state, int count, char signed_p) {
   // BUG: Does not 
   long long out = 0;
   int offset = 0;
+  int final_shift = 0;
   long long msb = (!!signed_p) << (count - 1); // 0 if unsigned, else 1 << (nbits - 1)
-  // BUG: does not stop early in case of
+  
+  
+  // overflow check...
+  int bits_left = (state->length - state->index); // well, bytes for now
+  if (bits_left <= 64) { // Large enough to handle any valid count, but small enough that overflow isn't a problem.
+    // not in danger of overflowing, so add in bits
+    // add in number of bits...
+    if (state->endianness & BIT_BIG_ENDIAN)
+      bits_left = (bits_left << 3) - 8 + state->bit_offset;
+    else
+      bits_left = (bits_left << 3) - state->bit_offset;
+    if (bits_left < count) {
+      if (state->endianness & BYTE_BIG_ENDIAN)
+	final_shift = count - bits_left;
+      else
+	final_shift = 0;
+      count = bits_left;
+      state->overrun = true;
+    } else
+      final_shift = 0;
+  }
   
   if ((state->bit_offset & 0x7) == 0 && (count & 0x7) == 0) {
     // fast path
     if (state->endianness & BYTE_BIG_ENDIAN) {
-      while (count > 0)
+      while (count > 0) {
+	count -= 8;
 	out = (out << 8) | state->input[state->index++];
+      }
     } else {
       while (count > 0) {
 	count -= 8;
@@ -65,6 +88,7 @@ long long read_bits(input_stream_t* state, int count, char signed_p) {
       count -= segment_len;
     }
   }
+  out <<= final_shift;
   return (out ^ msb) - msb; // perform sign extension
 }
 
diff --git a/src/hammer.c b/src/hammer.c
index 7d1dabb..0450f7d 100644
--- a/src/hammer.c
+++ b/src/hammer.c
@@ -72,6 +72,8 @@ parse_result_t* do_parse(const parser_t* parser, parse_state_t *state) {
     // It doesn't exist... run the 
     parse_result_t *res;
     res = parser->fn(parser->env, state);
+    if (state->input.overrun)
+      res = NULL; // overrun is always failure.
     // update the cache
     g_hash_table_replace(state->cache, &key, res);
 #ifdef CONSISTENCY_CHECK
diff --git a/src/hammer.h b/src/hammer.h
index b0a9c1a..e1afab6 100644
--- a/src/hammer.h
+++ b/src/hammer.h
@@ -41,6 +41,7 @@ typedef struct input_stream {
   size_t length;
   char bit_offset;
   char endianness;
+  char overrun;
 } input_stream_t;
   
 typedef struct parse_state {