diff --git a/CMakeLists.txt b/CMakeLists.txt
index 9a7e0b9..957ce05 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -25,7 +25,7 @@ find_package(Threads REQUIRED)
 
 # If using GCC, configure it accordingly.
 if (${CMAKE_C_COMPILER_ID} MATCHES GNU)
-  set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -Wall -Wextra -Wno-unused-parameter -std=c99 -Werror=implicit-function-declaration")
+  set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -fno-common -Wall -Wextra -Wno-unused-parameter -std=c99 -Werror=implicit-function-declaration")
 
   # Include architecture-specify machinery.
   execute_process(COMMAND ${CMAKE_C_COMPILER} -dumpmachine
diff --git a/ai/controller.h b/ai/controller.h
index 7f711fc..525a112 100644
--- a/ai/controller.h
+++ b/ai/controller.h
@@ -13,8 +13,6 @@
 #include "common.h"
 #include "ai/context.h"
 
-struct bus_controller *bus;
-
 enum ai_register {
 #define X(reg) reg,
 #include "ai/registers.md"
diff --git a/dd/controller.h b/dd/controller.h
index febce20..76fa13d 100644
--- a/dd/controller.h
+++ b/dd/controller.h
@@ -15,8 +15,6 @@
 #include "device/sha1.h"
 #include "os/common/rom_file.h"
 
-struct bus_controller *bus;
-
 enum dd_register {
 #define X(reg) reg,
 #include "dd/registers.md"
diff --git a/pi/controller.h b/pi/controller.h
index 16fb04a..f7a94cb 100644
--- a/pi/controller.h
+++ b/pi/controller.h
@@ -13,8 +13,6 @@
 #include "common.h"
 #include "os/common/save_file.h"
 
-struct bus_controller *bus;
-
 enum pi_register {
 #define X(reg) reg,
 #include "pi/registers.md"
diff --git a/ri/controller.h b/ri/controller.h
index e922903..b749406 100644
--- a/ri/controller.h
+++ b/ri/controller.h
@@ -14,8 +14,6 @@
 
 #define MAX_RDRAM_SIZE 0x800000U
 
-struct bus_controller *bus;
-
 enum rdram_register {
 #define X(reg) reg,
 #include "ri/rdram_registers.md"
diff --git a/si/controller.h b/si/controller.h
index 8acc03b..2e8a4ff 100644
--- a/si/controller.h
+++ b/si/controller.h
@@ -14,8 +14,6 @@
 #include "si/pak.h"
 #include "dd/controller.h"
 
-struct bus_controller *bus;
-
 enum si_register {
 #define X(reg) reg,
 #include "si/registers.md"
diff --git a/vi/controller.h b/vi/controller.h
index 0d50f65..bbe4c99 100644
--- a/vi/controller.h
+++ b/vi/controller.h
@@ -18,8 +18,6 @@
 #include "gl_window.h"
 #include "timer.h"
 
-struct bus_controller *bus;
-
 enum vi_register {
 #define X(reg) reg,
 #include "vi/registers.md"