diff --git a/src/core/peg.c b/src/core/peg.c
index d8ab0265..41c0ef19 100644
--- a/src/core/peg.c
+++ b/src/core/peg.c
@@ -211,6 +211,7 @@ tail:
         }
 
         case RULE_SET: {
+            if (text >= s->text_end) return NULL;
             uint32_t word = rule[1 + (text[0] >> 5)];
             uint32_t mask = (uint32_t)1 << (text[0] & 0x1F);
             return (text < s->text_end && (word & mask))
diff --git a/test/suite0013.janet b/test/suite0013.janet
index 1fd0bbdb..164e2cbb 100644
--- a/test/suite0013.janet
+++ b/test/suite0013.janet
@@ -27,4 +27,15 @@
 (assert (deep= (tabseq [i :in (range 3)] i)
                @{}))
 
+(def- sym-prefix-peg
+  (peg/compile
+    ~{:symchar (+ (range "\x80\xff" "AZ" "az" "09") (set "!$%&*+-./:<?=>@^_"))
+      :anchor (drop (cmt ($) ,|(= $ 0)))
+      :cap (* (+ (> -1 (not :symchar)) :anchor) (* ($) '(some :symchar)))
+      :recur (+ :cap (> -1 :recur))
+      :main (> -1 :recur)}))
+
+(assert (deep= (peg/match sym-prefix-peg @"123" 3) @[0 "123"]) "peg lookback")
+(assert (deep= (peg/match sym-prefix-peg @"1234" 4) @[0 "1234"]) "peg lookback 2")
+
 (end-suite)