diff --git a/src/bhyve/bhyve_firmware.c b/src/bhyve/bhyve_firmware.c
index cb1b94b4d5..ff131efa41 100644
--- a/src/bhyve/bhyve_firmware.c
+++ b/src/bhyve/bhyve_firmware.c
@@ -80,6 +80,13 @@ bhyveFirmwareFillDomain(bhyveConn *driver,
     if (!def->os.loader)
         def->os.loader = virDomainLoaderDefNew();
 
+    if (def->os.loader->format != VIR_STORAGE_FILE_RAW) {
+        virReportError(VIR_ERR_CONFIG_UNSUPPORTED,
+                       _("Unsupported loader format '%s'"),
+                       virStorageFileFormatTypeToString(def->os.loader->format));
+        return -1;
+    }
+
     def->os.loader->type = VIR_DOMAIN_LOADER_TYPE_PFLASH;
     def->os.loader->readonly = VIR_TRISTATE_BOOL_YES;
 
diff --git a/src/libxl/libxl_conf.c b/src/libxl/libxl_conf.c
index 97c183ebf3..485015ef63 100644
--- a/src/libxl/libxl_conf.c
+++ b/src/libxl/libxl_conf.c
@@ -656,6 +656,13 @@ libxlMakeDomBuildInfo(virDomainDef *def,
             b_info->u.hvm.bios = LIBXL_BIOS_TYPE_OVMF;
         }
 
+        if (def->os.loader && def->os.loader->format != VIR_STORAGE_FILE_RAW) {
+            virReportError(VIR_ERR_CONFIG_UNSUPPORTED,
+                           _("Unsupported loader format '%s'"),
+                           virStorageFileFormatTypeToString(def->os.loader->format));
+            return -1;
+        }
+
         if (def->emulator) {
             if (!virFileExists(def->emulator)) {
                 virReportError(VIR_ERR_CONFIG_UNSUPPORTED,
diff --git a/src/qemu/qemu_firmware.c b/src/qemu/qemu_firmware.c
index 4d34062ebf..be6d8d4519 100644
--- a/src/qemu/qemu_firmware.c
+++ b/src/qemu/qemu_firmware.c
@@ -1545,6 +1545,7 @@ qemuFirmwareFillDomain(virQEMUDriver *driver,
 {
     g_autoptr(virQEMUDriverConfig) cfg = virQEMUDriverGetConfig(driver);
     virDomainLoaderDef *loader = def->os.loader;
+    virStorageSource *nvram = loader ? loader->nvram : NULL;
     bool autoSelection = (def->os.firmware != VIR_DOMAIN_OS_DEF_FIRMWARE_NONE);
     int ret;
 
@@ -1559,6 +1560,21 @@ qemuFirmwareFillDomain(virQEMUDriver *driver,
     if (virDomainDefOSValidate(def, NULL) < 0)
         return -1;
 
+    if (loader &&
+        loader->format != VIR_STORAGE_FILE_RAW) {
+        virReportError(VIR_ERR_CONFIG_UNSUPPORTED,
+                       _("Unsupported loader format '%s'"),
+                       virStorageFileFormatTypeToString(loader->format));
+        return -1;
+    }
+    if (nvram &&
+        nvram->format != VIR_STORAGE_FILE_RAW) {
+        virReportError(VIR_ERR_CONFIG_UNSUPPORTED,
+                       _("Unsupported nvram format '%s'"),
+                       virStorageFileFormatTypeToString(nvram->format));
+        return -1;
+    }
+
     /* If firmware autoselection is disabled and the loader is a ROM
      * instead of a PFLASH device, then we're using BIOS and we don't
      * need any information at all */