diff --git a/drivers/media/video/bttv-risc.c b/drivers/media/video/bttv-risc.c
index b40e9734bf08..a60c211c9e31 100644
--- a/drivers/media/video/bttv-risc.c
+++ b/drivers/media/video/bttv-risc.c
@@ -51,8 +51,10 @@ bttv_risc_packed(struct bttv *btv, struct btcx_riscmem *risc,
 	int rc;
 
 	/* estimate risc mem: worst case is one write per page border +
-	   one write per scan line + sync + jump (all 2 dwords) */
-	instructions  = (bpl * lines) / PAGE_SIZE + lines;
+	   one write per scan line + sync + jump (all 2 dwords).  padding
+	   can cause next bpl to start close to a page border.  First DMA
+	   region may be smaller than PAGE_SIZE */
+	instructions  = 1 + ((bpl + padding) * lines) / PAGE_SIZE + lines;
 	instructions += 2;
 	if ((rc = btcx_riscmem_alloc(btv->c.pci,risc,instructions*8)) < 0)
 		return rc;
@@ -104,7 +106,7 @@ bttv_risc_packed(struct bttv *btv, struct btcx_riscmem *risc,
 
 	/* save pointer to jmp instruction address */
 	risc->jmp = rp;
-	BUG_ON((risc->jmp - risc->cpu + 2) / 4 > risc->size);
+	BUG_ON((risc->jmp - risc->cpu + 2) * sizeof(*risc->cpu) > risc->size);
 	return 0;
 }
 
@@ -222,7 +224,7 @@ bttv_risc_planar(struct bttv *btv, struct btcx_riscmem *risc,
 
 	/* save pointer to jmp instruction address */
 	risc->jmp = rp;
-	BUG_ON((risc->jmp - risc->cpu + 2) / 4 > risc->size);
+	BUG_ON((risc->jmp - risc->cpu + 2) * sizeof(*risc->cpu) > risc->size);
 	return 0;
 }
 
@@ -307,7 +309,7 @@ bttv_risc_overlay(struct bttv *btv, struct btcx_riscmem *risc,
 
 	/* save pointer to jmp instruction address */
 	risc->jmp = rp;
-	BUG_ON((risc->jmp - risc->cpu + 2) / 4 > risc->size);
+	BUG_ON((risc->jmp - risc->cpu + 2) * sizeof(*risc->cpu) > risc->size);
 	kfree(skips);
 	return 0;
 }
diff --git a/drivers/media/video/cx88/cx88-core.c b/drivers/media/video/cx88/cx88-core.c
index eda7cd8b2d4a..25be3a976d09 100644
--- a/drivers/media/video/cx88/cx88-core.c
+++ b/drivers/media/video/cx88/cx88-core.c
@@ -163,7 +163,7 @@ int cx88_risc_buffer(struct pci_dev *pci, struct btcx_riscmem *risc,
 
 	/* save pointer to jmp instruction address */
 	risc->jmp = rp;
-	BUG_ON((risc->jmp - risc->cpu + 2) / 4 > risc->size);
+	BUG_ON((risc->jmp - risc->cpu + 2) * sizeof (*risc->cpu) > risc->size);
 	return 0;
 }
 
@@ -188,7 +188,7 @@ int cx88_risc_databuffer(struct pci_dev *pci, struct btcx_riscmem *risc,
 
 	/* save pointer to jmp instruction address */
 	risc->jmp = rp;
-	BUG_ON((risc->jmp - risc->cpu + 2) / 4 > risc->size);
+	BUG_ON((risc->jmp - risc->cpu + 2) * sizeof (*risc->cpu) > risc->size);
 	return 0;
 }