diff --git a/simgear/math/SGTriangle.hxx b/simgear/math/SGTriangle.hxx
index af6f32f1..777b3788 100644
--- a/simgear/math/SGTriangle.hxx
+++ b/simgear/math/SGTriangle.hxx
@@ -16,7 +16,7 @@
 //
 
 #ifndef SGTriangle_H
-#define SGTrianlge_H
+#define SGTriangle_H
 
 template<typename T>
 class SGTriangle {