diff --git a/fcore/search-list/dfa-gen.sml b/fcore/search-list/dfa-gen.sml
index 6b1b96a..800a145 100644
--- a/fcore/search-list/dfa-gen.sml
+++ b/fcore/search-list/dfa-gen.sml
@@ -729,13 +729,21 @@ struct
           in
             Vector.concat [dtran, el]
           end
-        else
+        else if dStateIdx < Vector.length dtran then
           let
             val el = Vector.sub (dtran, dStateIdx)
             val el = Set.insertOrReplace (char, toStateIdx, el)
           in
             Vector.update (dtran, dStateIdx, el)
           end
+        else
+          let
+            val appendLength = dStateIdx - Vector.length dtran
+            val appendVecs = Vector.tabulate (appendLength, fn _ => Set.LEAF)
+            val dtran = Vector.concat [dtran, appendVecs]
+          in
+            insert (dStateIdx, char, toStateIdx, dtran)
+          end
     end
 
     fun convertChar
diff --git a/test/regression.sml b/test/regression.sml
index 4be552e..d3c4c79 100644
--- a/test/regression.sml
+++ b/test/regression.sml
@@ -67,6 +67,15 @@ struct
            in
              Expect.isTrue true
            end)
+    , test
+        "DfaGen does not cause exception \
+        \when parsing alternation that contains a char \
+        \from the previous alternation (1)"
+        (fn _ =>
+           (let val dfa = CaseSensitiveDfa.fromString "str|s"
+            in Expect.isTrue true
+            end)
+           handle _ => Expect.isTrue false)
     ]
 
   val tests = [charEventTests]