diff --git a/th01/main/playfld.hpp b/th01/main/playfld.hpp
index 441ba84e..2f2c14ff 100644
--- a/th01/main/playfld.hpp
+++ b/th01/main/playfld.hpp
@@ -1,20 +1,22 @@
-static const screen_x_t PLAYFIELD_LEFT = 0;
-static const screen_y_t PLAYFIELD_TOP = 64;
-static const screen_x_t PLAYFIELD_RIGHT = RES_X;
-static const screen_y_t PLAYFIELD_BOTTOM = RES_Y;
+#if (GAME == 1)
+	static const screen_x_t PLAYFIELD_LEFT = 0;
+	static const screen_y_t PLAYFIELD_TOP = 64;
+	static const screen_x_t PLAYFIELD_RIGHT = RES_X;
+	static const screen_y_t PLAYFIELD_BOTTOM = RES_Y;
 
-static const pixel_t PLAYFIELD_W = (PLAYFIELD_RIGHT - PLAYFIELD_LEFT);
-static const pixel_t PLAYFIELD_H = (PLAYFIELD_BOTTOM - PLAYFIELD_TOP);
+	static const pixel_t PLAYFIELD_W = (PLAYFIELD_RIGHT - PLAYFIELD_LEFT);
+	static const pixel_t PLAYFIELD_H = (PLAYFIELD_BOTTOM - PLAYFIELD_TOP);
 
-static const screen_x_t PLAYFIELD_CENTER_X = (
-	((PLAYFIELD_RIGHT - PLAYFIELD_LEFT) / 2) + PLAYFIELD_LEFT
-);
+	static const screen_x_t PLAYFIELD_CENTER_X = (
+		((PLAYFIELD_RIGHT - PLAYFIELD_LEFT) / 2) + PLAYFIELD_LEFT
+	);
 
-static const screen_y_t PLAYFIELD_CENTER_Y = (
-	((PLAYFIELD_BOTTOM - PLAYFIELD_TOP) / 2) + PLAYFIELD_TOP
-);
+	static const screen_y_t PLAYFIELD_CENTER_Y = (
+		((PLAYFIELD_BOTTOM - PLAYFIELD_TOP) / 2) + PLAYFIELD_TOP
+	);
+#endif
 
-inline pixel_t playfield_fraction_x(float fraction = 1.0f) {
+static inline pixel_t playfield_fraction_x(float fraction = 1.0f) {
 	return ((int)(PLAYFIELD_W * fraction));
 }
 
diff --git a/th02/formats/mpn_l_i.cpp b/th02/formats/mpn_l_i.cpp
index f8216e5b..c85238aa 100644
--- a/th02/formats/mpn_l_i.cpp
+++ b/th02/formats/mpn_l_i.cpp
@@ -6,7 +6,7 @@ extern "C" {
 #include "pc98.h"
 #include "planar.h"
 #include "master.hpp"
-#include "th02/main/playfld.h"
+#include "th02/main/playfld.hpp"
 #include "th02/main/tile.hpp"
 #include "th02/formats/mpn.hpp"
 
diff --git a/th02/main/playfld.h b/th02/main/playfld.hpp
similarity index 96%
rename from th02/main/playfld.h
rename to th02/main/playfld.hpp
index 31a6e316..00149fc6 100644
--- a/th02/main/playfld.h
+++ b/th02/main/playfld.hpp
@@ -23,3 +23,5 @@
 	// (Future games use a near function.)
 	void far playfield_tram_wipe(void);
 #endif
+
+#include "th01/main/playfld.hpp"
diff --git a/th02/main02_1.cpp b/th02/main02_1.cpp
index 01c050be..d4beb26c 100644
--- a/th02/main02_1.cpp
+++ b/th02/main02_1.cpp
@@ -11,7 +11,7 @@ extern "C" {
 #include "pc98.h"
 #include "planar.h"
 #include "master.hpp"
-#include "th02/main/playfld.h"
+#include "th02/main/playfld.hpp"
 #include "th02/main/tile.hpp"
 #include "th02/formats/mpn.hpp"
 
diff --git a/th04/formats/mpn_free.cpp b/th04/formats/mpn_free.cpp
index 523f5069..0036c4b7 100644
--- a/th04/formats/mpn_free.cpp
+++ b/th04/formats/mpn_free.cpp
@@ -6,7 +6,7 @@ extern "C" {
 #include "pc98.h"
 #include "planar.h"
 #include "master.hpp"
-#include "th04/main/playfld.h"
+#include "th04/main/playfld.hpp"
 #include "th04/main/tile.hpp"
 #include "th04/formats/mpn.hpp"
 
diff --git a/th04/formats/mpn_l_i.cpp b/th04/formats/mpn_l_i.cpp
index 05c24167..7f216cf3 100644
--- a/th04/formats/mpn_l_i.cpp
+++ b/th04/formats/mpn_l_i.cpp
@@ -7,7 +7,7 @@ extern "C" {
 #include "pc98.h"
 #include "planar.h"
 #include "master.hpp"
-#include "th04/main/playfld.h"
+#include "th04/main/playfld.hpp"
 #include "th04/main/tile.hpp"
 #include "th04/formats/mpn.hpp"
 
diff --git a/th04/main/hud/popup.cpp b/th04/main/hud/popup.cpp
index 615b825d..39080c8f 100644
--- a/th04/main/hud/popup.cpp
+++ b/th04/main/hud/popup.cpp
@@ -9,7 +9,7 @@
 #include "th04/hardware/grcg.h"
 #include "th04/math/motion.hpp"
 #include "th04/main/null.hpp"
-#include "th04/main/playfld.h"
+#include "th04/main/playfld.hpp"
 #include "th04/main/tile.hpp"
 #include "th04/main/scroll.hpp"
 #include "th04/main/hud/popup.hpp"
diff --git a/th04/main/playfld.h b/th04/main/playfld.hpp
similarity index 88%
rename from th04/main/playfld.h
rename to th04/main/playfld.hpp
index 6b63df6c..365d1d2f 100644
--- a/th04/main/playfld.h
+++ b/th04/main/playfld.hpp
@@ -1,4 +1,4 @@
-#include "th02/main/playfld.h"
+#include "th02/main/playfld.hpp"
 
 // Fills the playfield area on the text RAM with transparent spaces.
 void near playfield_tram_wipe(void);
diff --git a/th04/shared.hpp b/th04/shared.hpp
index 0f01538d..6f0cd350 100644
--- a/th04/shared.hpp
+++ b/th04/shared.hpp
@@ -24,7 +24,7 @@
 #include "th04/score.h"
 /// ------
 
-#include "th04/main/playfld.h"
+#include "th04/main/playfld.hpp"
 
 /// Stages
 /// ------
diff --git a/th05/main/boss/b4_both.cpp b/th05/main/boss/b4_both.cpp
index 389d4246..813e308b 100644
--- a/th05/main/boss/b4_both.cpp
+++ b/th05/main/boss/b4_both.cpp
@@ -3,7 +3,6 @@
  * Update code for Part 1 of the Stage 4 boss fight, against both Mai and Yuki
  */
 
-#include "th04/main/playfld.h"
 #include "th04/math/vector.hpp"
 #include "th05/sprites/main_pat.h"
 
diff --git a/th05/main/boss/render.cpp b/th05/main/boss/render.cpp
index 25c6cf63..0eb28a36 100644
--- a/th05/main/boss/render.cpp
+++ b/th05/main/boss/render.cpp
@@ -9,7 +9,7 @@
 #include "th01/math/subpixel.hpp"
 #include "th04/math/vector.hpp"
 #include "th04/main/drawp.hpp"
-#include "th04/main/playfld.h"
+#include "th04/main/playfld.hpp"
 
 /// Structures
 /// ----------
diff --git a/th05/main/player/bombanim.cpp b/th05/main/player/bombanim.cpp
index a2e1bf29..33a4e2e7 100644
--- a/th05/main/player/bombanim.cpp
+++ b/th05/main/player/bombanim.cpp
@@ -3,7 +3,7 @@
 #include "th01/math/subpixel.hpp"
 #include "th04/math/vector.hpp"
 #include "th04/math/randring.h"
-#include "th04/main/playfld.h"
+#include "th04/main/playfld.hpp"
 #include "th04/main/frames.h"
 #include "th04/main/circles.hpp"
 #include "th05/sprites/main_pat.h"
diff --git a/th05/main034.cpp b/th05/main034.cpp
index 69270602..da43be43 100644
--- a/th05/main034.cpp
+++ b/th05/main034.cpp
@@ -9,7 +9,7 @@ extern "C" {
 #include "ReC98.h"
 #include "th01/math/subpixel.hpp"
 #include "th01/math/area.hpp"
-#include "th04/main/playfld.h"
+#include "th04/main/playfld.hpp"
 #include "th04/math/motion.hpp"
 #include "th05/main/boss/boss.hpp"
 #include "th05/main/boss/bx.cpp"