diff --git a/src/swrenderer/r_swcanvas.cpp b/src/swrenderer/r_swcanvas.cpp
index 564fa8ca5..5522d89dc 100644
--- a/src/swrenderer/r_swcanvas.cpp
+++ b/src/swrenderer/r_swcanvas.cpp
@@ -401,7 +401,7 @@ void SWCanvas::DrawLine(DCanvas *canvas, int x0, int y0, int x1, int y1, int pal
 		palColor = PalFromRGB(realcolor);
 	}
 
-	canvas->Lock(true);
+	canvas->Lock();
 	int deltaX, deltaY, xDir;
 
 	if (y0 > y1)
diff --git a/src/swrenderer/r_swrenderer.cpp b/src/swrenderer/r_swrenderer.cpp
index 25b3539d1..9f842d38e 100644
--- a/src/swrenderer/r_swrenderer.cpp
+++ b/src/swrenderer/r_swrenderer.cpp
@@ -207,6 +207,7 @@ void FSoftwareRenderer::WriteSavePic (player_t *player, FileWriter *file, int wi
 	PalEntry palette[256];
 
 	// Take a snapshot of the player's view
+	pic.Lock ();
 	if (r_polyrenderer)
 	{
 		PolyRenderer::Instance()->Viewpoint = r_viewpoint;
@@ -225,6 +226,7 @@ void FSoftwareRenderer::WriteSavePic (player_t *player, FileWriter *file, int wi
 	}
 	screen->GetFlashedPalette (palette);
 	M_CreatePNG (file, pic.GetBuffer(), palette, SS_PAL, width, height, pic.GetPitch(), Gamma);
+	pic.Unlock ();
 }
 
 void FSoftwareRenderer::DrawRemainingPlayerSprites()
diff --git a/src/swrenderer/scene/r_scene.cpp b/src/swrenderer/scene/r_scene.cpp
index b229367ee..0fd292d69 100644
--- a/src/swrenderer/scene/r_scene.cpp
+++ b/src/swrenderer/scene/r_scene.cpp
@@ -380,7 +380,9 @@ namespace swrenderer
 		R_ExecuteSetViewSize(MainThread()->Viewport->viewpoint, MainThread()->Viewport->viewwindow);
 		float trueratio;
 		ActiveRatio(width, height, &trueratio);
+		screen->Lock(true);
 		viewport->SetViewport(MainThread(), width, height, trueratio);
+		screen->Unlock();
 
 		viewactive = savedviewactive;
 	}
@@ -393,7 +395,9 @@ namespace swrenderer
 		int height = SCREENHEIGHT;
 		float trueratio;
 		ActiveRatio(width, height, &trueratio);
+		screen->Lock(true);
 		viewport->SetViewport(MainThread(), SCREENWIDTH, SCREENHEIGHT, trueratio);
+		screen->Unlock();
 	}
 
 	void RenderScene::Init()