diff --git a/changelogs/unreleased/gh-6375-fix-assert-on-unsupported-ext.md b/changelogs/unreleased/gh-6375-fix-assert-on-unsupported-ext.md
new file mode 100644
index 0000000000000000000000000000000000000000..c68251239ed0f9c3e85d5ea6193823c4fa263413
--- /dev/null
+++ b/changelogs/unreleased/gh-6375-fix-assert-on-unsupported-ext.md
@@ -0,0 +1,5 @@
+## bugfix/sql
+
+* Now getting unsupported msgpack extension in SQL will throw correct
+  error (gh-6375).
+
diff --git a/src/box/sql/mem.c b/src/box/sql/mem.c
index 0aca761125d3e31f81e72bb82e8e46b6ad4a0fff..4c40f15dc3f9a39ebf76f7ec07387fc350c6af16 100644
--- a/src/box/sql/mem.c
+++ b/src/box/sql/mem.c
@@ -3484,12 +3484,15 @@ port_lua_get_vdbemem(struct port *base, uint32_t *size)
 				goto error;
 			break;
 		case MP_EXT: {
-			assert(field.ext_type == MP_UUID ||
-			       field.ext_type == MP_DECIMAL);
-			if (field.ext_type == MP_UUID)
+			if (field.ext_type == MP_UUID) {
 				mem_set_uuid(&val[i], field.uuidval);
-			else
+			} else if (field.ext_type == MP_DECIMAL) {
 				mem_set_dec(&val[i], field.decval);
+			} else {
+				diag_set(ClientError, ER_SQL_EXECUTE,
+					 "Unsupported type passed from Lua");
+				goto error;
+			}
 			break;
 		}
 		case MP_NIL:
diff --git a/test/sql-tap/engine.cfg b/test/sql-tap/engine.cfg
index 35754f769d4951570e88ebb3c71e5bff6b3be7c3..587adbed9e32ee966e0cfc772d79e55feb9488d6 100644
--- a/test/sql-tap/engine.cfg
+++ b/test/sql-tap/engine.cfg
@@ -36,6 +36,7 @@
         "memtx": {"engine": "memtx"}
     },
     "gh-4077-iproto-execute-no-bind.test.lua": {},
+    "gh-6375-assert-on-unsupported-ext.test.lua": {},
     "*": {
         "memtx": {"engine": "memtx"},
         "vinyl": {"engine": "vinyl"}
diff --git a/test/sql-tap/gh-6375-assert-on-unsupported-ext.test.lua b/test/sql-tap/gh-6375-assert-on-unsupported-ext.test.lua
new file mode 100755
index 0000000000000000000000000000000000000000..35980c58eb8794a6c874bd0a54cd326fde6a5399
--- /dev/null
+++ b/test/sql-tap/gh-6375-assert-on-unsupported-ext.test.lua
@@ -0,0 +1,25 @@
+#!/usr/bin/env tarantool
+local test = require("sqltester")
+test:plan(2)
+
+--
+-- Make sure that the correct error occurs when unsupported extension is
+-- received by SQL.
+--
+test:do_catchsql_test(
+    "gh-6375-1",
+    [[
+        SELECT LUA('return box.space._vindex:select()[1]');
+    ]], {
+        1, "Failed to execute SQL statement: Unsupported type passed from Lua"
+    })
+
+test:do_catchsql_test(
+    "gh-6375-2",
+    [[
+        SELECT 1 > LUA('return box.space._vindex:select()[1]');
+    ]], {
+        1, "Failed to execute SQL statement: Unsupported type passed from Lua"
+    })
+
+test:finish_test()