diff --git a/configure.ac b/configure.ac
index 0b2d1320..11d84584 100644
--- a/configure.ac
+++ b/configure.ac
@@ -123,14 +123,13 @@ AC_TRY_LINK([asm("_glibc_foobar:");], [glibc_foobar()], [
 
 dnl ---------------------------------------------------------------------------
 
+# Sometimes Flex is installed as Lex, e.g., NetBSD.
+AC_CHECK_PROG([FLEX], [flex lex], [flex])
+# Force the use of `missing' to wrap Flex invocations.
+AM_MISSING_PROG([LEX], [$FLEX])
+# Perform all the tests Automake and Autoconf need.
 AM_PROG_LEX
 
-dnl AS_IF([test "x$LEX" = "xno"], [
-dnl     AC_MSG_ERROR([Emulator needs lex/flex to build source...])
-dnl ], [
-dnl     AC_MSG_RESULT([Found lex $LEX])
-dnl ])
-
 dnl POSIX high-precision clock
 AC_SEARCH_LIBS(clock_gettime, rt, [], [
     AC_MSG_ERROR([Emulator needs realtime clocks (-lrt) to build...])