diff --git a/gnu/packages/bioinformatics.scm b/gnu/packages/bioinformatics.scm
index 7dc1bc48cedc43e97c44c947dcf0c0f63c4e8e69..1c5a5c2eeb473d7fdb7cdb8e443d719246d7eb34 100644
--- a/gnu/packages/bioinformatics.scm
+++ b/gnu/packages/bioinformatics.scm
@@ -1658,6 +1658,7 @@ (define-public vcftools
     (arguments
      `(#:tests? #f ; no "check" target
        #:make-flags (list
+                     "CFLAGS=-O2" ; override "-m64" flag
                      (string-append "PREFIX=" (assoc-ref %outputs "out"))
                      (string-append "MANDIR=" (assoc-ref %outputs "out")
                                     "/share/man/man1"))