diff --git a/tests/t_lpback.sh b/tests/t_lpback.sh
index fb43211d..dd6c34e5 100755
--- a/tests/t_lpback.sh
+++ b/tests/t_lpback.sh
@@ -77,10 +77,15 @@ else
     echo "OK"
 fi
 
+# Generate max-length base64 metadata ('A' is 0b000000 in base64)
+METADATA=""
+for i in $(seq 1 732); do
+    METADATA="${METADATA}A"
+done
 echo -n "Testing tls-crypt-v2 key generation (max length metadata)..."
 "${top_builddir}/src/openvpn/openvpn" --tls-crypt-v2 tc-server-key.$$ \
-    --tls-crypt-v2-genkey client tc-client-key.$$ \
-    $(head -c732 /dev/zero | base64 -w0) >log.$$ 2>&1
+    --tls-crypt-v2-genkey client tc-client-key.$$ "${METADATA}" \
+    >log.$$ 2>&1
 if [ $? != 0 ] ; then
     echo "FAILED"
     cat log.$$