diff --git a/src/qemu/qemu_command.c b/src/qemu/qemu_command.c
index 693d30da47..29424d6d80 100644
--- a/src/qemu/qemu_command.c
+++ b/src/qemu/qemu_command.c
@@ -5228,6 +5228,7 @@ qemuBuildMachineArgStr(virCommandPtr cmd,
                 virReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s",
                                _("dump-guest-core is not available "
                                  "with this QEMU binary"));
+                virBufferFreeAndReset(&buf);
                 return -1;
             }