diff --git a/wadsrc/static/zscript/shared/fastprojectile.txt b/wadsrc/static/zscript/shared/fastprojectile.txt
index c861a3f8f..4ba05a7bf 100644
--- a/wadsrc/static/zscript/shared/fastprojectile.txt
+++ b/wadsrc/static/zscript/shared/fastprojectile.txt
@@ -66,13 +66,21 @@ class FastProjectile : Actor
 		int count = 8;
 		if (radius > 0)
 		{
-			while ( abs(Vel.X) >= radius * count || abs(Vel.Y) >= radius * count || abs(Vel.Z) >= height * count)
+			while (abs(Vel.X) >= radius * count || abs(Vel.Y) >= radius * count)
 			{
 				// we need to take smaller steps.
 				count += count;
 			}
 		}
 
+		if (height > 0)
+		{
+			while (abs(Vel.Z) >= height * count)
+			{
+				count += count;
+			}
+		}
+
 		// Handle movement
 		if (Vel != (0, 0, 0) || (pos.Z != floorz))
 		{