diff --git a/sw/tools/gen_aircraft.ml b/sw/tools/gen_aircraft.ml
index 72b25931d4..7e0f1efaba 100644
--- a/sw/tools/gen_aircraft.ml
+++ b/sw/tools/gen_aircraft.ml
@@ -232,7 +232,12 @@ let parse_firmware = fun makefile_ac firmware ->
     (* print makefile for this target *)
     fprintf makefile_ac "\n###########\n# -target: '%s'\n" (Xml.attrib target "name");
     fprintf makefile_ac "ifeq ($(TARGET), %s)\n" (Xml.attrib target "name");
-    try fprintf makefile_ac "BOARD_PROCESSOR = %s\n" (Xml.attrib target "processor") with _ -> ();
+    let has_processor =
+      try
+        not (String.compare (Xml.attrib target "processor") "" = 0)
+      with _ -> false in
+    if has_processor then
+      fprintf makefile_ac "BOARD_PROCESSOR = %s\n" (Xml.attrib target "processor");
     List.iter (print_firmware_configure makefile_ac) config;
     List.iter (print_firmware_configure makefile_ac) t_config;
     List.iter (print_firmware_define makefile_ac) defines;