diff --git a/source/libs/opl.h b/source/libs/opl.h
index 0da880c..56bf013 100644
--- a/source/libs/opl.h
+++ b/source/libs/opl.h
@@ -6,7 +6,7 @@
 opl.h - v0.1 - OPL3 (SoundBlaster16) emulation with MIDI compatible interface
 
 Do this:
-    #define OP_IMPLEMENTATION
+    #define OPL_IMPLEMENTATION
 before you include this file in *one* C/C++ file to create the implementation.
 
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