diff --git a/source/core/gamefuncs.h b/source/core/gamefuncs.h
index 6b659a4bb..b1d531905 100644
--- a/source/core/gamefuncs.h
+++ b/source/core/gamefuncs.h
@@ -523,4 +523,10 @@ inline DAngle ClampViewPitch(const DAngle pitch)
 	return clamp(pitch, GetMaxPitch(), GetMinPitch());
 }
 
+inline void setFreeAimVelocity(double& vel, double& zvel, const DAngle pitch, const double zvspeed)
+{
+	vel *= pitch.Cos();
+	zvel = pitch.Sin() * zvspeed;
+}
+
 #include "updatesector.h"
diff --git a/source/games/duke/src/player_d.cpp b/source/games/duke/src/player_d.cpp
index b4ea750c7..0a6fc550f 100644
--- a/source/games/duke/src/player_d.cpp
+++ b/source/games/duke/src/player_d.cpp
@@ -683,7 +683,7 @@ static void shootrpg(DDukeActor *actor, int p, DVector3 pos, DAngle ang, int atw
 				ang = (aimed->spr.pos.XY() - pos.XY()).Angle();
 		}
 		else 
-			zvel = ps[p].horizon.sum().Tan() * 40.5;
+			setFreeAimVelocity(vel, zvel, ps[p].horizon.sum(), 40.5);
 
 		if (atwith == RPG)
 			S_PlayActorSound(RPG_SHOOT, actor);