diff --git a/src/engine.cpp b/src/engine.cpp
index a0bacae..f4b118a 100644
--- a/src/engine.cpp
+++ b/src/engine.cpp
@@ -25,7 +25,7 @@ engine::engine(const std::string& start,
     _verbosity_level {verbose}
 {
     // setup random distribution
-    _dist.param(std::uniform_int_distribution<>::param_type {0, static_cast<int>(_numerals.size())});
+    _dist.param(std::uniform_int_distribution<>::param_type {0, static_cast<int>(_numerals.size()) - 1});
     
     // now we know how many numerals we have, so we can allocate our efficient buffers
     unsigned int n;
@@ -54,7 +54,7 @@ engine::engine(const std::string& start,
     
     // get letter frequencies from sentence start
     for (char c : start) {
-        // optionally translate upper- to lowercase
+        // translate upper- to lowercase
         const char up_lo_dif = 'a' - 'A';
         if (c >= 'A' && c <= 'Z') {
             c += up_lo_dif;
@@ -129,17 +129,20 @@ void engine::run()
 
             // count letters in resulting sentence by incrementing result freqmap elements
             for (n = 0; n < 26; n++) {
+#if DEBUG
                 if (static_cast<unsigned int>(prev[n]) < _numerals.size()) {
+#endif
                     auto p = freq[prev[n]];
                     for (k = 0; k < 26; k++) {
                         next[k] += p[k];
                     }
+#if DEBUG
                 } else {
-                    // FIXME continuously reports overflow
-                    // char c = 'a' + n;
-                    // std::cerr << std::endl << "overflow: " << c << " (" << prev[n] << ")";
-                    // break;
+                    char c = 'a' + n;
+                    std::cerr << std::endl << "overflow: " << c << " (" << prev[n] << ")";
+                    break;
                 }
+#endif
             }
 
             // increment frequency for 's' for every letter which occurs more than once,