diff --git a/autogen.pl b/autogen.pl
index aa12a1d1bf..58b44785b6 100755
--- a/autogen.pl
+++ b/autogen.pl
@@ -56,11 +56,13 @@ my $exclude_list;
 my $ompi_automake_version = "1.11.1";
 my $ompi_autoconf_version = "2.65";
 my $ompi_libtool_version = "2.2.6b";
+my $ompi_flex_version = "2.5.35";
 
 # Search paths
 my $ompi_autoconf_search = "autoconf";
 my $ompi_automake_search = "automake";
 my $ompi_libtoolize_search = "libtoolize;glibtoolize";
+my $ompi_flex_search = "flex";
 
 # One-time setup
 my $username;
@@ -797,6 +799,7 @@ GNU tools:
     GNU Autoconf: $ompi_autoconf_version
     GNU Automake: $ompi_automake_version
     GNU Libtool: $ompi_libtool_version
+    Flex: $ompi_flex_version
 =================================================================\n";
     my_exit(1);
 }
@@ -1015,6 +1018,7 @@ $step. Checking tool versions\n\n";
 &find_and_check("autoconf", $ompi_autoconf_search, $ompi_autoconf_version);
 &find_and_check("libtool", $ompi_libtoolize_search, $ompi_libtool_version);
 &find_and_check("automake", $ompi_automake_search, $ompi_automake_version);
+&find_and_check("flex", $ompi_flex_search, $ompi_flex_version);
 
 #---------------------------------------------------------------------------