diff --git a/vars/build.vars b/vars/build.vars
index fac64b1..c7319a2 100644
--- a/vars/build.vars
+++ b/vars/build.vars
@@ -182,6 +182,7 @@ HOST_TOOLS_PREFIX="${PREFIX}";
 : ${PKG_BISON_HOST_SHA256SUM:=55e4a023b1b4ad19095a5f8279f0dc048fa29f970759cea83224a6d5e7a3a641};
 : ${PKG_BISON_HOST_VERSION:=3.5};
 : ${PKG_BISON_HOST_URL:=https://ftp.gnu.org/gnu/bison/bison-${PKG_BISON_HOST_VERSION}.tar.xz};
+: ${PKG_BISON_HOST_ENV_VARS_EXTRA:="M4=${PREFIX}/bin/m4"};
 : ${PKG_FLEX_HOST_SHA256SUM:=68b2742233e747c462f781462a2a1e299dc6207401dac8f0bbb316f48565c2aa};
 : ${PKG_FLEX_HOST_VERSION:=2.6.3};
 : ${PKG_FLEX_HOST_URL:=https://github.com/westes/flex/releases/download/v${PKG_FLEX_HOST_VERSION}/flex-${PKG_FLEX_HOST_VERSION}.tar.gz};