diff --git a/projectile.s b/projectile.s
index 710e86b..67cb1c7 100644
--- a/projectile.s
+++ b/projectile.s
@@ -939,7 +939,7 @@ processTerrainImpactStoreContinue:
 	adc projectileTypes+PT_RADIUS,y
 	adc #GAMEOBJECTWIDTH
 	sta compileTerrainRowEnd
-;don't forget to clamp these to terrain edges'
+
 	lda projectileTypes+PT_RADIUS,y
 	tay
 	phy					; We'll need the radius in a moment
diff --git a/terrain.s b/terrain.s
index dce122e..b500cca 100644
--- a/terrain.s
+++ b/terrain.s
@@ -295,12 +295,19 @@ compileTerrainDone:
 ; Trashes A,Y, SCRATCHL, PARAML0, PARAML1
 ;
 compileTerrainChunk:
-	ldy #0
-	tya			; Be extra safe and make sure Y is never negative or we'll spray RAM with terrain data
+	
+	; Clamp chunk to left and right terrain edges
+	lda compileTerrainRowStart
 	bmi compileTerrainChunkClampZero
-	ldx #MAXTERRAINHEIGHT-1
+
+compileTerrainChunkClampResume:
+	lda compileTerrainRowEnd
+	cmp #TERRAINWIDTH
+	bcs compileTerrainChunkClampHigh
 
 compileTerrainChunkResume:
+	ldy #0
+	ldx #MAXTERRAINHEIGHT-1
 	stx SCRATCHL
 	sty PARAML0
 
@@ -329,9 +336,13 @@ compileTerrainChunkDone:
 	rts
 
 compileTerrainChunkClampZero:
-	ldy #0
-	bra compileTerrainChunkResume
+	stz compileTerrainRowStart
+	bra compileTerrainChunkClampResume
 
+compileTerrainChunkClampHigh:
+	lda #TERRAINWIDTH-1
+	sta compileTerrainRowEnd
+	bra compileTerrainChunkResume
 
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 ; compileTerrainRow