diff --git a/src/include/cpu/x86/mtrr.h b/src/include/cpu/x86/mtrr.h
index 017a77e..913ba47 100644
--- a/src/include/cpu/x86/mtrr.h
+++ b/src/include/cpu/x86/mtrr.h
@@ -92,6 +92,10 @@
 
 #endif
 
+#if !defined(__ASSEMBLER__) && defined(__PRE_RAM__) && !defined(__ROMCC__)
+void set_var_mtrr(unsigned reg, unsigned base, unsigned size, unsigned type);
+#endif
+
 #if !defined(CONFIG_RAMTOP)
 # error "CONFIG_RAMTOP not defined"
 #endif