diff --git a/th04/main/bullet/bullet.hpp b/th04/main/bullet/bullet.hpp
index eb61b4e7..93f48316 100644
--- a/th04/main/bullet/bullet.hpp
+++ b/th04/main/bullet/bullet.hpp
@@ -164,11 +164,14 @@ static const subpixel_t BULLET_KILLBOX_H = TO_SP(8);
 # define PELLET_COUNT 180
 # define BULLET16_COUNT 220
 
-// Returns the patnum for the directional or vector bullet sprite starting at
-// [patnum_base] that shows the given [angle].
-int pascal near bullet_patnum_for_angle(int patnum_base, unsigned char angle);
-// Updates [bullet]'s patnum based on its current angle.
-void pascal near bullet_update_patnum(bullet_t near &bullet);
+// Returns the sprite ID of a directional or vector bullet sprite that
+// represents the given [angle], relative to [patnum_base]. While the function
+// is technically not restricted to `main_patnum_t` in TH05 and can also be
+// used for a general (angle / BULLET_D_CELS) division, it still assumes
+// [patnum_base] to be that type in order to distinguish vector bullets.
+unsigned char pascal near bullet_patnum_for_angle(
+	int patnum_base, unsigned char angle
+);
 
 // Turns every 4th bullet into a point item when zapping bullets.
 extern bool bullet_zap_drop_point_items;
diff --git a/th04/main/bullet/update.cpp b/th04/main/bullet/update.cpp
index c00ac1e1..a71611d8 100644
--- a/th04/main/bullet/update.cpp
+++ b/th04/main/bullet/update.cpp
@@ -30,6 +30,26 @@ extern "C" {
 	#include "th05/sprites/main_pat.h"
 
 	static const int SLOWDOWN_BULLET_THRESHOLD_UNUSED = 32;
+
+	// Updates [bullet]'s patnum based on its current angle.
+	void pascal near bullet_update_patnum(bullet_t near &bullet)
+	{
+		unsigned char patnum_base; // main_patnum_t, obviously
+
+		if(bullet.patnum < PAT_BULLET16_D) {
+			return;
+		}
+		if(bullet.patnum < (PAT_BULLET16_D_BLUE_last + 1)) {
+			patnum_base = PAT_BULLET16_D_BLUE;
+		} else if(bullet.patnum < (PAT_BULLET16_D_GREEN_last + 1)) {
+			patnum_base = PAT_BULLET16_D_GREEN;
+		} else if(bullet.patnum < (PAT_BULLET16_V_RED_last + 1)) {
+			patnum_base = PAT_BULLET16_V_RED;
+		} else {
+			patnum_base = PAT_BULLET16_V_BLUE;
+		}
+		bullet.patnum = bullet_patnum_for_angle(patnum_base, bullet.angle);
+	}
 #else
 	#include "th04/sprites/main_pat.h"
 
diff --git a/th05/main/bullet/update_patnum.asm b/th05/main/bullet/update_patnum.asm
deleted file mode 100644
index a372d43d..00000000
--- a/th05/main/bullet/update_patnum.asm
+++ /dev/null
@@ -1,48 +0,0 @@
-public BULLET_UPDATE_PATNUM
-bullet_update_patnum	proc near
-
-@@patnum_base	= byte ptr -1
-@@bullet     	= word ptr  4
-
-	push	bp
-	mov	bp, sp
-	sub	sp, 2
-	push	si
-	mov	si, [bp+@@bullet]
-	cmp	[si+bullet_t.BULLET_patnum], PAT_BULLET16_D_BLUE
-	jl	short @@ret
-	cmp	[si+bullet_t.BULLET_patnum], PAT_BULLET16_D_GREEN
-	jge	short @@d_green?
-	mov	[bp+@@patnum_base], PAT_BULLET16_D_BLUE
-	jmp	short @@set
-; ---------------------------------------------------------------------------
-
-@@d_green?:
-	cmp	[si+bullet_t.BULLET_patnum], PAT_BULLET16_V_RED
-	jge	short @@v_red?
-	mov	[bp+@@patnum_base], PAT_BULLET16_D_GREEN
-	jmp	short @@set
-; ---------------------------------------------------------------------------
-
-@@v_red?:
-	cmp	[si+bullet_t.BULLET_patnum], PAT_BULLET16_V_BLUE
-	jge	short @@v_blue?
-	mov	[bp+@@patnum_base], PAT_BULLET16_V_RED
-	jmp	short @@set
-; ---------------------------------------------------------------------------
-
-@@v_blue?:
-	mov	[bp+@@patnum_base], PAT_BULLET16_V_BLUE
-
-@@set:
-	mov	al, [bp+@@patnum_base]
-	mov	ah, 0
-	call	bullet_patnum_for_angle pascal, ax, word ptr [si+bullet_t.BULLET_angle]
-	mov	ah, 0
-	mov	[si+bullet_t.BULLET_patnum], ax
-
-@@ret:
-	pop	si
-	leave
-	retn	2
-bullet_update_patnum	endp
diff --git a/th05_main.asm b/th05_main.asm
index 0d9b73d1..c503ee11 100644
--- a/th05_main.asm
+++ b/th05_main.asm
@@ -11594,7 +11594,6 @@ loc_178A5:
 curvebullets_update	endp
 
 include th04/main/item/splashes_update.asm
-include th05/main/bullet/update_patnum.asm
 	extern _bullets_update:proc
 main_033_TEXT	ends