diff --git a/shellpki b/shellpki
index f255180..f1b4b1f 100755
--- a/shellpki
+++ b/shellpki
@@ -49,7 +49,7 @@ Create a client certificate with key and CSR directly generated on server :
         -p, --password              prompt the user for a password to set on the client key
             --password-file         if provided with a path to a readable file, the first line is read and set as password on the client key
             --days                  specify how many days the certificate should be valid
-            --end-date              specify until which date the certificate should be valid, in MM/DD/[YY]YY [hh:mm:ss] format
+            --end-date              specify until which date the certificate should be valid, in "MM/DD/YYYY hh:mm:ss" format
             --non-interactive       do not prompt the user, and exit if an error occurs
             --replace-existing      if the certificate already exists, revoke it before creating a new one
 
@@ -490,12 +490,24 @@ create() {
         crt_expiration_arg="-days ${days}"
     fi
     if [ -n "${end_date}" ]; then
-        cert_end_date=$(TZ=:Zulu date --date "${end_date}" +"%Y%m%d%H%M%SZ" 2> /dev/null)
-        # shellcheck disable=SC2181
-        if [ "$?" -ne 0 ]; then
-            error "Invalid end date format : \`${end_date}' can't be parsed by date(1)"
+        if [ "${SYSTEM}" = "linux" ]; then
+            cert_end_date=$(TZ=:Zulu date --date "${end_date}" +"%Y%m%d%H%M%SZ" 2> /dev/null)
+            # shellcheck disable=SC2181
+            if [ "$?" -ne 0 ]; then
+                error "Invalid end date format: \`${end_date}' can't be parsed by date(1). Expected format: MM/DD/[YY]YY [hh[:mm[:ss]]]."
+            else
+                crt_expiration_arg="-enddate ${cert_end_date}"
+            fi
+        elif [ "${SYSTEM}" = "openbsd" ]; then
+            cert_end_date=$(TZ=:Zulu date -f "%m/%d/%C%y %H:%M:%S" -j "${end_date}" +"%Y%m%d%H%M%SZ" 2> /dev/null)
+            # shellcheck disable=SC2181
+            if [ "$?" -ne 0 ]; then
+                error "Invalid end date format: \`${end_date}' can't be parsed by date(1). Expected format: MM/DD/YYYY hh:mm:ss."
+            else
+                crt_expiration_arg="-enddate ${cert_end_date}"
+            fi
         else
-            crt_expiration_arg="-enddate ${cert_end_date}"
+            error "System ${SYSTEM} not supported."
         fi
     fi
     if [ "${non_interactive}" -eq 1 ]; then
@@ -901,6 +913,9 @@ is_group() {
 }
 
 main() {
+    # Know what system we are on, because OpenBSD and Linux do not implement date(1) in the same way
+    SYSTEM=$(uname | tr '[:upper:]' '[:lower:]')
+
     # default config
     # TODO : override with /etc/default/shellpki
     CONF_FILE="/etc/shellpki/openssl.cnf"