diff --git a/bochs/instrument/stubs/instrument.cc b/bochs/instrument/stubs/instrument.cc
index ccdd002cf..e36556b88 100644
--- a/bochs/instrument/stubs/instrument.cc
+++ b/bochs/instrument/stubs/instrument.cc
@@ -24,6 +24,8 @@
 
 #if BX_INSTRUMENTATION
 
+class bxInstruction_c;
+
 void bx_instr_init_env(void) {}
 void bx_instr_exit_env(void) {}