diff --git a/asm/assembler/assembler.c b/asm/assembler/assembler.c
index 719edd8..11c1b8f 100644
--- a/asm/assembler/assembler.c
+++ b/asm/assembler/assembler.c
@@ -287,7 +287,7 @@ enum ivy_status ivy_assembler_end_scope(struct ivy_assembler *as)
 
 enum ivy_status ivy_assembler_put_pval(
 	struct ivy_assembler *as, enum ivy_assembler_pval_type type,
-	const void *val, ivy_extended_data_key *key)
+	size_t slot, const void *val, ivy_extended_data_key *key)
 {
 	struct assembler_scope *scope = as->as_scope;
 
@@ -300,7 +300,7 @@ enum ivy_status ivy_assembler_put_pval(
 		return IVY_ERR_NOT_SUPPORTED;
 	}
 
-	return type_info->s_put_pval(as, scope, type, val, key);
+	return type_info->s_put_pval(as, scope, type, slot, val, key);
 }
 
 enum ivy_status ivy_assembler_put_xval(
diff --git a/asm/assembler/assembler.h b/asm/assembler/assembler.h
index 40f2a9d..4519fda 100644
--- a/asm/assembler/assembler.h
+++ b/asm/assembler/assembler.h
@@ -27,7 +27,7 @@ struct assembler_scope_type {
 
 	enum ivy_status (*s_put_pval)(
 		struct ivy_assembler *, struct assembler_scope *,
-		enum ivy_assembler_pval_type, const void *,
+		enum ivy_assembler_pval_type, size_t, const void *,
 		ivy_extended_data_key *key);
 
 	enum ivy_status (*s_put_xval)(
diff --git a/asm/assembler/constpool.c b/asm/assembler/constpool.c
index de20b2d..11e56a1 100644
--- a/asm/assembler/constpool.c
+++ b/asm/assembler/constpool.c
@@ -13,6 +13,7 @@
 struct constpool_assembler_scope {
 	struct assembler_scope s_base;
 	b_dict *s_strings;
+	size_t s_next_slot;
 };
 
 static enum ivy_status init_scope(
@@ -26,6 +27,7 @@ static enum ivy_status init_scope(
 	struct constpool_assembler_scope *c
 		= (struct constpool_assembler_scope *)scope;
 	c->s_strings = b_dict_create();
+	c->s_next_slot = 0;
 
 	return IVY_OK;
 }
@@ -151,12 +153,18 @@ static ivy_extended_data_key write_ident(
 
 static enum ivy_status put_pval(
 	struct ivy_assembler *as, struct assembler_scope *scope,
-	enum ivy_assembler_pval_type type, const void *val,
+	enum ivy_assembler_pval_type type, size_t slot, const void *val,
 	ivy_extended_data_key *key)
 {
 	struct ivy_bin_constpool_table_entry entry = {0};
 	uintptr_t i = *(uintptr_t *)val;
 	ivy_extended_data_key k = IVY_EX_DATA_KEY_NULL;
+	struct constpool_assembler_scope *s
+		= (struct constpool_assembler_scope *)assembler_get_scope(as);
+
+	if (slot < s->s_next_slot) {
+		return IVY_ERR_NAME_EXISTS;
+	}
 
 	switch (type) {
 	case IVY_ASM_PVAL_STRING:
@@ -195,7 +203,13 @@ static enum ivy_status put_pval(
 		*key = k;
 	}
 
+	for (size_t i = s->s_next_slot; i < slot; i++) {
+		struct ivy_bin_constpool_table_entry null_entry = {0};
+		assembler_write_data(as, &null_entry, sizeof null_entry);
+	}
+
 	assembler_write_data(as, &entry, sizeof entry);
+	s->s_next_slot = slot + 1;
 	return IVY_OK;
 }
 
diff --git a/asm/include/ivy/asm/assembler.h b/asm/include/ivy/asm/assembler.h
index 7dae232..fab521d 100644
--- a/asm/include/ivy/asm/assembler.h
+++ b/asm/include/ivy/asm/assembler.h
@@ -72,7 +72,7 @@ IVY_API enum ivy_status ivy_assembler_end_scope(struct ivy_assembler *as);
 
 IVY_API enum ivy_status ivy_assembler_put_pval(
 	struct ivy_assembler *as, enum ivy_assembler_pval_type type,
-	const void *val, ivy_extended_data_key *key);
+	size_t slot, const void *val, ivy_extended_data_key *key);
 IVY_API enum ivy_status ivy_assembler_put_xval(
 	struct ivy_assembler *as, enum ivy_assembler_xval_type type,
 	const ivy_assembler_attrib_table attrib);