diff --git a/src/servers/src/mysql/handler.rs b/src/servers/src/mysql/handler.rs
index 587742687d82..d84a5945cabb 100644
--- a/src/servers/src/mysql/handler.rs
+++ b/src/servers/src/mysql/handler.rs
@@ -189,8 +189,6 @@ impl MysqlInstanceShim {
             dummy_params(param_num)?
         };
 
-        debug_assert_eq!(params.len(), param_num - 1);
-
         let columns = schema
             .as_ref()
             .map(|schema| {
@@ -205,14 +203,26 @@ impl MysqlInstanceShim {
             .transpose()?
             .unwrap_or_default();
 
-        self.save_plan(
-            SqlPlan {
-                query: query.to_string(),
-                plan,
-                schema,
-            },
-            stmt_key,
-        );
+        // DataFusion may optimize the plan so that some parameters are not used.
+        if params.len() != param_num - 1 {
+            self.save_plan(
+                SqlPlan {
+                    query: query.to_string(),
+                    plan: None,
+                    schema: None,
+                },
+                stmt_key,
+            );
+        } else {
+            self.save_plan(
+                SqlPlan {
+                    query: query.to_string(),
+                    plan,
+                    schema,
+                },
+                stmt_key,
+            );
+        }
 
         Ok((params, columns))
     }
diff --git a/tests/cases/standalone/common/prepare/mysql_prepare.result b/tests/cases/standalone/common/prepare/mysql_prepare.result
new file mode 100644
index 000000000000..ae6ca4400cab
--- /dev/null
+++ b/tests/cases/standalone/common/prepare/mysql_prepare.result
@@ -0,0 +1,72 @@
+-- invalid prepare, from
+-- https://github.com/duckdb/duckdb/blob/00a605270719941ca0412ad5d0a14b1bdfbf9eb5/test/sql/prepared/invalid_prepare.test
+-- SQLNESS PROTOCOL MYSQL
+SELECT ?;
+
+Failed to execute query, err: MySqlError { ERROR 1815 (HY000): (PlanQuery): Failed to plan SQL: Error during planning: Placeholder type could not be resolved. Make sure that the placeholder is bound to a concrete type, e.g. by providing parameter values. }
+
+-- SQLNESS PROTOCOL MYSQL
+PREPARE stmt FROM 'SELECT ?::int;';
+
+affected_rows: 0
+
+-- SQLNESS PROTOCOL MYSQL
+EXECUTE stmt USING 1;
+
++----------+
+| Int64(1) |
++----------+
+| 1        |
++----------+
+
+-- SQLNESS PROTOCOL MYSQL
+EXECUTE stmt USING 'a';
+
+Failed to parse query result, err: MySqlError { ERROR 1815 (HY000): (EngineExecuteQuery): Cast error: Cannot cast string 'a' to value of Int32 type }
+
+-- SQLNESS PROTOCOL MYSQL
+DEALLOCATE stmt;
+
+affected_rows: 0
+
+-- SQLNESS PROTOCOL MYSQL
+PREPARE stmt FROM 'SELECT ?::int WHERE 1=0;';
+
+affected_rows: 0
+
+-- SQLNESS PROTOCOL MYSQL
+EXECUTE stmt USING 1;
+
+affected_rows: 0
+
+-- SQLNESS PROTOCOL MYSQL
+EXECUTE stmt USING 'a';
+
+affected_rows: 0
+
+-- SQLNESS PROTOCOL MYSQL
+DEALLOCATE stmt;
+
+affected_rows: 0
+
+-- parameter variants, from:
+-- https://github.com/duckdb/duckdb/blob/2360dd00f193b5d0850f9379d0c3794eb2084f36/test/sql/prepared/parameter_variants.test
+-- SQLNESS PROTOCOL MYSQL
+PREPARE stmt FROM 'SELECT CAST(? AS INTEGER), CAST(? AS STRING);';
+
+affected_rows: 0
+
+-- SQLNESS PROTOCOL MYSQL
+EXECUTE stmt USING 1, 'hello';
+
++----------+---------------+
+| Int64(1) | Utf8("hello") |
++----------+---------------+
+| 1        | hello         |
++----------+---------------+
+
+-- SQLNESS PROTOCOL MYSQL
+DEALLOCATE stmt;
+
+affected_rows: 0
+
diff --git a/tests/cases/standalone/common/prepare/mysql_prepare.sql b/tests/cases/standalone/common/prepare/mysql_prepare.sql
new file mode 100644
index 000000000000..da1681a790ff
--- /dev/null
+++ b/tests/cases/standalone/common/prepare/mysql_prepare.sql
@@ -0,0 +1,39 @@
+-- invalid prepare, from
+-- https://github.com/duckdb/duckdb/blob/00a605270719941ca0412ad5d0a14b1bdfbf9eb5/test/sql/prepared/invalid_prepare.test
+-- SQLNESS PROTOCOL MYSQL
+SELECT ?;
+
+-- SQLNESS PROTOCOL MYSQL
+PREPARE stmt FROM 'SELECT ?::int;';
+
+-- SQLNESS PROTOCOL MYSQL
+EXECUTE stmt USING 1;
+
+-- SQLNESS PROTOCOL MYSQL
+EXECUTE stmt USING 'a';
+
+-- SQLNESS PROTOCOL MYSQL
+DEALLOCATE stmt;
+
+-- SQLNESS PROTOCOL MYSQL
+PREPARE stmt FROM 'SELECT ?::int WHERE 1=0;';
+
+-- SQLNESS PROTOCOL MYSQL
+EXECUTE stmt USING 1;
+
+-- SQLNESS PROTOCOL MYSQL
+EXECUTE stmt USING 'a';
+
+-- SQLNESS PROTOCOL MYSQL
+DEALLOCATE stmt;
+
+-- parameter variants, from:
+-- https://github.com/duckdb/duckdb/blob/2360dd00f193b5d0850f9379d0c3794eb2084f36/test/sql/prepared/parameter_variants.test
+-- SQLNESS PROTOCOL MYSQL
+PREPARE stmt FROM 'SELECT CAST(? AS INTEGER), CAST(? AS STRING);';
+
+-- SQLNESS PROTOCOL MYSQL
+EXECUTE stmt USING 1, 'hello';
+
+-- SQLNESS PROTOCOL MYSQL
+DEALLOCATE stmt;