diff --git a/linker/linker_environ.h b/linker/linker_environ.h
index cd7a65b..d3f54fd 100644
--- a/linker/linker_environ.h
+++ b/linker/linker_environ.h
@@ -29,7 +29,7 @@
 #ifndef LINKER_ENVIRON_H
 #define LINKER_ENVIRON_H
 
-struct KernelArgumentBlock;
+class KernelArgumentBlock;
 
 // Call this function before any of the other functions in this header file.
 extern void linker_env_init(KernelArgumentBlock& args);