diff --git a/src/mame/video/ms1_tmap.cpp b/src/mame/video/ms1_tmap.cpp
index 0523e64664c..0d7b25f9d97 100644
--- a/src/mame/video/ms1_tmap.cpp
+++ b/src/mame/video/ms1_tmap.cpp
@@ -129,6 +129,16 @@ void megasys1_tilemap_device::device_start()
 	save_item(NAME(m_scroll_flag));
 }
 
+void megasys1_tilemap_device::device_reset()
+{
+	// Big Run never sets up scrollram past 0x1000
+	// this causes its opaque pen to show up when the game scrolls vertically after a bump.
+	// we initialize the device VRAM to a sane default so that this doesn't occur.
+	// TODO: might be something else (smaller VRAM size?)
+	for(int i=0;i<m_scrollram.bytes()/2;i++)
+		m_scrollram[i] = 0xffff;
+}
+
 void megasys1_tilemap_device::device_post_load()
 {
 	m_tmap = m_tilemap[(m_scroll_flag >> 4) & 1][m_scroll_flag & 3];
diff --git a/src/mame/video/ms1_tmap.h b/src/mame/video/ms1_tmap.h
index a66dea660ac..bfb2a6853fd 100644
--- a/src/mame/video/ms1_tmap.h
+++ b/src/mame/video/ms1_tmap.h
@@ -66,6 +66,7 @@ public:
 protected:
 	// device-level overrides
 	virtual void device_start() override;
+	virtual void device_reset() override;
 	virtual void device_post_load() override;
 
 private: