diff --git a/Dockerfile b/Dockerfile
index cf83412..874e58d 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -20,7 +20,7 @@ RUN \
   if [ "$ADDITIONAL_CA_URL" != "x" ]; then \
     cd /usr/share/ca-certificates; \
     wget --no-check-certificate -O custom-ca.crt $ADDITIONAL_CA_URL; \
-    echo "a$ADDITIONAL_CA_CHECKSUM  custom-ca.crt" | md5sum -c; \
+    echo "$ADDITIONAL_CA_CHECKSUM  custom-ca.crt" | md5sum -c; \
     /usr/sbin/update-ca-certificates; \
     echo "custom ca added"; \
   else \