diff --git a/src/gl/models/gl_models.cpp b/src/gl/models/gl_models.cpp
index 541a4c36c1..963518a991 100644
--- a/src/gl/models/gl_models.cpp
+++ b/src/gl/models/gl_models.cpp
@@ -53,9 +53,9 @@
 #include "gl/renderer/gl_renderstate.h"
 #include "gl/shaders/gl_shader.h"
 
-static inline float GetTimeFloat()
+static inline double GetTimeFloat()
 {
-	return (float)screen->FrameTime * (float)TICRATE / 1000.0f;
+	return (double)screen->FrameTime * (double)TICRATE / 1000.;
 }
 
 CVAR(Bool, gl_interpolate_model_frames, true, CVAR_ARCHIVE)
@@ -890,7 +890,7 @@ void gl_RenderFrameModels( const FSpriteModelFrame *smf,
 			// [BB] In case the tic counter is frozen we have to leave ticFraction at zero.
 			if ( ConsoleState == c_up && menuactive != MENU_On && !(level.flags2 & LEVEL2_FROZEN) )
 			{
-				float time = GetTimeFloat();
+				double time = GetTimeFloat();
 				ticFraction = (time - static_cast<int>(time));
 			}
 			inter = static_cast<double>(curState->Tics - curTics - ticFraction)/static_cast<double>(curState->Tics);
@@ -999,8 +999,8 @@ void gl_RenderModel(GLSprite * spr)
 
 	if( smf->flags & MDL_ROTATING )
 	{
-		const float time = smf->rotationSpeed*GetTimeFloat()/200.f;
-		rotateOffset = float((time - xs_FloorToInt(time)) *360.f );
+		const double time = smf->rotationSpeed*GetTimeFloat()/200.;
+		rotateOffset = double((time - xs_FloorToInt(time)) *360. );
 	}
 
 	// Added MDL_USEACTORPITCH and MDL_USEACTORROLL flags processing.
diff --git a/src/gl/renderer/gl_renderstate.cpp b/src/gl/renderer/gl_renderstate.cpp
index 1427e23501..5385e4ae37 100644
--- a/src/gl/renderer/gl_renderstate.cpp
+++ b/src/gl/renderer/gl_renderstate.cpp
@@ -118,6 +118,10 @@ void FRenderState::Reset()
 
 bool FRenderState::ApplyShader()
 {
+	static int firstFrame = 0;
+	if (firstFrame == 0)
+		firstFrame = screen->FrameTime;
+
 	static const float nulvec[] = { 0.f, 0.f, 0.f, 0.f };
 	if (mSpecialEffect > EFF_NONE)
 	{
@@ -161,7 +165,7 @@ bool FRenderState::ApplyShader()
 	activeShader->muInterpolationFactor.Set(mInterpolationFactor);
 	activeShader->muClipHeight.Set(mClipHeight);
 	activeShader->muClipHeightDirection.Set(mClipHeightDirection);
-	activeShader->muTimer.Set(screen->FrameTime * mShaderTimer / 1000.f);
+	activeShader->muTimer.Set((double)(screen->FrameTime - firstFrame) * mShaderTimer / 1000.f);
 	activeShader->muAlphaThreshold.Set(mAlphaThreshold);
 	activeShader->muLightIndex.Set(mLightIndex);	// will always be -1 for now
 	activeShader->muClipSplit.Set(mClipSplit);
diff --git a/src/gl/scene/gl_scene.cpp b/src/gl/scene/gl_scene.cpp
index 92d3785213..329ac64840 100644
--- a/src/gl/scene/gl_scene.cpp
+++ b/src/gl/scene/gl_scene.cpp
@@ -800,8 +800,8 @@ sector_t * GLSceneDrawer::RenderViewpoint (AActor * camera, GL_IRECT * bounds, f
 	GLRenderer->mAngles.Roll.Degrees = r_viewpoint.Angles.Roll.Degrees;
 
 	// Scroll the sky
-	GLRenderer->mSky1Pos = (float)fmod(screen->FrameTime * level.skyspeed1, 1024.f) * 90.f/256.f;
-	GLRenderer->mSky2Pos = (float)fmod(screen->FrameTime * level.skyspeed2, 1024.f) * 90.f/256.f;
+	GLRenderer->mSky1Pos = (double)fmod(screen->FrameTime * level.skyspeed1, 1024.f) * 90./256.;
+	GLRenderer->mSky2Pos = (double)fmod(screen->FrameTime * level.skyspeed2, 1024.f) * 90./256.;
 
 
 
diff --git a/src/i_time.cpp b/src/i_time.cpp
index 050bb1ebc9..4be0a8b826 100644
--- a/src/i_time.cpp
+++ b/src/i_time.cpp
@@ -60,9 +60,9 @@ static uint64_t MSToNS(unsigned int ms)
 	return static_cast<uint64_t>(ms) * 1'000'000;
 }
 
-static uint32_t NSToMS(uint64_t ns)
+static uint64_t NSToMS(uint64_t ns)
 {
-	return static_cast<uint32_t>(ns / 1'000'000);
+	return static_cast<uint64_t>(ns / 1'000'000);
 }
 
 static int NSToTic(uint64_t ns)
@@ -125,7 +125,7 @@ uint64_t I_nsTime()
 	return GetClockTimeNS();
 }
 
-unsigned int I_msTime()
+uint64_t I_msTime()
 {
 	return NSToMS(I_nsTime());
 }
diff --git a/src/i_time.h b/src/i_time.h
index 1605969698..33907ded2a 100644
--- a/src/i_time.h
+++ b/src/i_time.h
@@ -20,7 +20,7 @@ int I_WaitForTic(int);
 void I_FreezeTime(bool frozen);
 
 // [RH] Returns millisecond-accurate time
-unsigned int I_msTime();
+uint64_t I_msTime();
 
 // Nanosecond-accurate time
 uint64_t I_nsTime();
diff --git a/src/v_video.h b/src/v_video.h
index 5934a3706a..4fae94198e 100644
--- a/src/v_video.h
+++ b/src/v_video.h
@@ -453,7 +453,7 @@ public:
 	// The original size of the framebuffer as selected in the video menu.
 	int VideoWidth = 0;
 	int VideoHeight = 0;
-	uint32_t FrameTime = 0;
+	uint64_t FrameTime = 0;
 
 protected:
 	void DrawRateStuff ();