diff --git a/sys/geom/part/g_part.c b/sys/geom/part/g_part.c
index 71c0b05cce07..ad8495694140 100644
--- a/sys/geom/part/g_part.c
+++ b/sys/geom/part/g_part.c
@@ -535,8 +535,8 @@ g_part_ctl_bootcode(struct gctl_req *req, struct g_part_parms *gpp)
 		error = ENODEV;
 		goto fail;
 	}
-	if (gpp->gpp_codesize != sz) {
-		error = EINVAL;
+	if (gpp->gpp_codesize > sz) {
+		error = EFBIG;
 		goto fail;
 	}
 
diff --git a/sys/geom/part/g_part_gpt.c b/sys/geom/part/g_part_gpt.c
index 7bdfa077fcb2..13a45617434b 100644
--- a/sys/geom/part/g_part_gpt.c
+++ b/sys/geom/part/g_part_gpt.c
@@ -374,9 +374,14 @@ static int
 g_part_gpt_bootcode(struct g_part_table *basetable, struct g_part_parms *gpp)
 {
 	struct g_part_gpt_table *table;
+	size_t codesz;
 
+	codesz = DOSPARTOFF;
 	table = (struct g_part_gpt_table *)basetable;
-	bcopy(gpp->gpp_codeptr, table->mbr, DOSPARTOFF);
+	bzero(table->mbr, codesz);
+	codesz = MIN(codesz, gpp->gpp_codesize);
+	if (codesz > 0)
+		bcopy(gpp->gpp_codeptr, table->mbr, codesz);
 	return (0);
 }
 
diff --git a/sys/geom/part/g_part_mbr.c b/sys/geom/part/g_part_mbr.c
index 9e3e809c7d51..b0ba3231f7fa 100644
--- a/sys/geom/part/g_part_mbr.c
+++ b/sys/geom/part/g_part_mbr.c
@@ -213,9 +213,14 @@ static int
 g_part_mbr_bootcode(struct g_part_table *basetable, struct g_part_parms *gpp)
 {
 	struct g_part_mbr_table *table;
+	size_t codesz;
 
+	codesz = DOSPARTOFF;
 	table = (struct g_part_mbr_table *)basetable;
-	bcopy(gpp->gpp_codeptr, table->mbr, DOSPARTOFF);
+	bzero(table->mbr, codesz);
+	codesz = MIN(codesz,  gpp->gpp_codesize);
+	if (codesz > 0)
+		bcopy(gpp->gpp_codeptr, table->mbr, codesz);
 	return (0);
 }
 
diff --git a/sys/geom/part/g_part_pc98.c b/sys/geom/part/g_part_pc98.c
index 2b997bcad5fb..f0f14747eca7 100644
--- a/sys/geom/part/g_part_pc98.c
+++ b/sys/geom/part/g_part_pc98.c
@@ -209,9 +209,14 @@ static int
 g_part_pc98_bootcode(struct g_part_table *basetable, struct g_part_parms *gpp)
 {
 	struct g_part_pc98_table *table;
+	size_t codesz;
 
+	codesz = DOSMAGICOFFSET;
 	table = (struct g_part_pc98_table *)basetable;
-	bcopy(gpp->gpp_codeptr, table->boot, DOSMAGICOFFSET);
+	bzero(table->boot, codesz);
+	codesz = MIN(codesz, gpp->gpp_codesize);
+	if (codesz > 0)
+		bcopy(gpp->gpp_codeptr, table->boot, codesz);
 	return (0);
 }