diff --git a/gnu/packages/flex.scm b/gnu/packages/flex.scm
index bc4498b633..22c309ec23 100644
--- a/gnu/packages/flex.scm
+++ b/gnu/packages/flex.scm
@@ -56,14 +56,10 @@
               (inputs (alist-delete "flex" (package-inputs bison))))))
        `(("bison" ,bison-for-tests))))
     (arguments
-     (if (or (target-hurd64?) (%current-target-system))
+     (if (%current-target-system)
          (list #:configure-flags
                #~'("ac_cv_func_malloc_0_nonnull=yes"
-                   "ac_cv_func_realloc_0_nonnull=yes"
-                   #$(string-append
-                      "CFLAGS=-g -O2"
-                      " -Wno-error=implicit-function-declaration"
-                      " -Wno-error=int-conversion")))
+                   "ac_cv_func_realloc_0_nonnull=yes"))
          '()))
     ;; m4 is not present in PATH when cross-building
     (native-inputs