Index: compiler/generator.c
===================================================================
--- compiler/generator.c	(revision 425)
+++ compiler/generator.c	(working copy)
@@ -884,23 +884,25 @@
     int empty_case = -1;
     int n_cases = 0;
     symbol cases[2];
-    int shortest_size = INT_MAX; /* Only if p->mode == m_forward */
+    int shortest_size = INT_MAX;
 
     g->S[0] = p->mode == m_forward ? "" : "_b";
     g->I[0] = x->number;
     g->I[1] = x->literalstring_count;
 
-    if (p->mode == m_forward) {
     /* In forward mode with non-ASCII UTF-8 characters, the first character
      * of the string will often be the same, so instead look at the last
-     * common character position. */
+     * common character position.
+     *
+     * In backward mode, we can't match if there are fewer characters before
+     * the current position than the minimum length.
+     */
     for (c = 0; c < x->literalstring_count; ++c) {
         int size = among_cases[c].size;
         if (size != 0 && size < shortest_size) {
             shortest_size = size;
         }
     }
-    }
 
     for (c = 0; c < x->literalstring_count; ++c) {
         symbol ch;
@@ -941,14 +943,22 @@
     char buf[64];
     g->I[2] = block;
     g->I[3] = bitmap;
+    g->I[4] = shortest_size - 1;
     if (p->mode == m_forward) {
         sprintf(buf, "z->p[z->c + %d]", shortest_size - 1);
         g->S[1] = buf;
-        g->I[4] = shortest_size - 1;
-        wp(g, "~Mif (z->c + ~I4 >= z->l || ", p);
+	if (shortest_size == 1) {
+	    wp(g, "~Mif (z->c >= z->l || ", p);
+	} else {
+	    wp(g, "~Mif (z->c + ~I4 >= z->l || ", p);
+	}
     } else {
         g->S[1] = "z->p[z->c - 1]";
-        wp(g, "~Mif (z->c <= z->lb || ", p);
+	if (shortest_size == 1) {
+	    wp(g, "~Mif (z->c <= z->lb || ", p);
+	} else {
+	    wp(g, "~Mif (z->c - ~I4 <= z->lb || ", p);
+	}
     }
     if (n_cases == 0) {
         /* We get this for the degenerate case: among { '' }