diff --git a/Source/cmCommandArgumentLexer.cxx b/Source/cmCommandArgumentLexer.cxx
index 4881171bc..d58d125b1 100644
--- a/Source/cmCommandArgumentLexer.cxx
+++ b/Source/cmCommandArgumentLexer.cxx
@@ -1046,6 +1046,7 @@ case YY_STATE_EOF(NOESCAPES):
                         "fatal flex scanner internal error--no action found" );
         } /* end of action switch */
                 } /* end of scanning one token */
+return 0; /* this should not happend but it should silence a warning */
 } /* end of cmCommandArgument_yylex */
 
 /* yy_get_next_buffer - try to read in a new buffer
diff --git a/Source/cmDependsJavaLexer.cxx b/Source/cmDependsJavaLexer.cxx
index a168a7d27..3af688adb 100644
--- a/Source/cmDependsJavaLexer.cxx
+++ b/Source/cmDependsJavaLexer.cxx
@@ -1596,6 +1596,7 @@ case YY_STATE_EOF(string):
       "fatal flex scanner internal error--no action found" );
   } /* end of action switch */
     } /* end of scanning one token */
+return 0; /* this should not happen but it silences a warning*/
 } /* end of cmDependsJava_yylex */
 
 /* yy_get_next_buffer - try to read in a new buffer
diff --git a/Source/cmExprLexer.cxx b/Source/cmExprLexer.cxx
index 6183804a8..a53b5c9a5 100644
--- a/Source/cmExprLexer.cxx
+++ b/Source/cmExprLexer.cxx
@@ -981,6 +981,7 @@ case YY_STATE_EOF(INITIAL):
       "fatal flex scanner internal error--no action found" );
   } /* end of action switch */
     } /* end of scanning one token */
+return 0; /* this should not happen but it silences a warning*/
 } /* end of cmExpr_yylex */
 
 /* yy_get_next_buffer - try to read in a new buffer