diff --git a/configure.sh b/configure.sh
index d1b5aa24..51d99b6f 100755
--- a/configure.sh
+++ b/configure.sh
@@ -77,8 +77,8 @@ GUILE=${GUILE-$(command -v guile)} || true
 HEX2=${HEX2-$(command -v hex2)}
 LDPFLAGS=${LDFLAGS-}
 M1=${M1-$(command -v M1)}
-M2_PLANET=${M1-$(command -v M2-Planet)}
-KAEM=${KAEM-$(command -v kaem)}
+M2_PLANET=${M2_PLANET-$(command -v M2-Planet)} || true
+KAEM=${KAEM-$(command -v kaem)} || true
 MES_FOR_BUILD=${MES_FOR_BUILD-$(command -v mes || command -v guile || echo mes)}
 GIT=${GIT-$(command -v git)} || true
 PERL=${PERL-$(command -v perl)} || true