diff --git a/PIL/ImageMode.py b/PIL/ImageMode.py
index 3587cec24..583fd7eda 100644
--- a/PIL/ImageMode.py
+++ b/PIL/ImageMode.py
@@ -39,6 +39,7 @@ def getmode(mode):
         for m, (basemode, basetype, bands) in Image._MODEINFO.items():
             _modes[m] = ModeDescriptor(m, bands, basemode, basetype)
         # extra experimental modes
+        _modes["RGBa"] = ModeDescriptor("RGBa", ("R", "G", "B", "a"), "RGB", "L")
         _modes["LA"] = ModeDescriptor("LA", ("L", "A"), "L", "L")
         _modes["La"] = ModeDescriptor("La", ("L", "a"), "L", "L")
         _modes["PA"] = ModeDescriptor("PA", ("P", "A"), "RGB", "L")