diff --git a/meta/classes-recipe/image_types.bbclass b/meta/classes-recipe/image_types.bbclass
index e6ef0ce11e..326602d960 100644
--- a/meta/classes-recipe/image_types.bbclass
+++ b/meta/classes-recipe/image_types.bbclass
@@ -44,6 +44,10 @@ def imagetypes_getdepends(d):
                 deprecated.add(var)
 
         for ctype in resttypes:
+            ctype_cmd = d.getVar('CONVERSION_CMD:' + ctype)
+            if not ctype_cmd:
+                bb.fatal('No CONVERSION_CMD defined for subtype "%s"'
+                         ' - possibly invalid conversion type name or missing support class' % ctype)
             adddep(d.getVar("CONVERSION_DEPENDS_%s" % ctype), deps)
             adddep(d.getVar("COMPRESS_DEPENDS_%s" % ctype), deps)