diff --git a/openvpn.c b/openvpn.c
index 1e33c61..10e3f30 100644
--- a/openvpn.c
+++ b/openvpn.c
@@ -1432,6 +1432,11 @@ OnPassword(connection_t *c, char *msg)
             param->flags |= (flags & 0x2) ? FLAG_CR_TYPE_CONCAT : FLAG_CR_TYPE_SCRV1;
             param->flags |= (flags & 0x1) ? FLAG_CR_ECHO : 0;
             param->str = strdup(chstr + 5);
+            if (!param->str)
+            {
+                WriteStatusLog(c, L"GUI> ", L"Error: Out of memory - ignoring dynamic challenge", false);
+                return;
+            }
             LocalizedDialogBoxParamEx(ID_DLG_AUTH_CHALLENGE, c->hwndStatus, UserAuthDialogFunc, (LPARAM) param);
         }
         else if (o.auth_pass_concat_otp)