diff --git a/configure1.in b/configure1.in
index ee633c8f0b7..07978375461 100755
--- a/configure1.in
+++ b/configure1.in
@@ -1176,7 +1176,10 @@ if test "${HAVE_X11}" = "yes"; then
 fi
 
 AC_ALLOCA
-AC_HAVE_FUNCS(gettimeofday gethostname dup2 rename closedir mkdir rmdir random bcopy)
+
+# logb and frexp are found in -lm on most systems.
+AC_HAVE_LIBRARY(-lm)
+AC_HAVE_FUNCS(gettimeofday gethostname dup2 rename closedir mkdir rmdir random bcopy logb frexp)
 
 ok_so_far=true
 AC_FUNC_CHECK(socket, , ok_so_far=)