diff --git a/core/interfaces/i_procedure_block.js b/core/interfaces/i_procedure_block.js
new file mode 100644
index 000000000..17502c19a
--- /dev/null
+++ b/core/interfaces/i_procedure_block.js
@@ -0,0 +1,43 @@
+/**
+ * @license
+ * Copyright 2021 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+/**
+ * @fileoverview The interface for a procedure block.
+ */
+
+'use strict';
+
+goog.provide('Blockly.Procedures.ProcedureBlock');
+
+/**
+ * A procedure block interface.
+ * @interface
+ */
+Blockly.Procedures.ProcedureBlock = function() {};
+
+/**
+ * Returns the name of the procedure the procedure block calls.
+ * @return {string}
+ */
+Blockly.Procedures.ProcedureBlock.prototype.getProcedureCall;
+
+/**
+ * Renames the procedure from the old name to the new name. If the procedure
+ * block receives this and the old name matches the block's current name, it
+ * should update itself to have the new name instead.
+ * @param {string} oldName The old name of the procedure.
+ * @param {string} newName The new name of hte procedure.
+ */
+Blockly.Procedures.ProcedureBlock.prototype.renameProcedure;
+
+/**
+ * Returns the signature of the procedure block's procedure definition.
+ * @return {!Array} Tuple containing three elements:
+ *     - {string} the name of the defined procedure
+ *     - {!Array<string>} a list of all its arguments
+ *     - {boolean} whether it has a return value or not
+ */
+Blockly.Procedures.ProcedureBlock.prototype.getProcedureDef;
diff --git a/core/procedures.js b/core/procedures.js
index 59c364719..03b0210b3 100644
--- a/core/procedures.js
+++ b/core/procedures.js
@@ -25,6 +25,7 @@ goog.require('Blockly.Events.BlockChange');
 goog.require('Blockly.Field');
 goog.require('Blockly.Msg');
 goog.require('Blockly.Names');
+goog.require('Blockly.Procedures.ProcedureBlock');
 goog.require('Blockly.utils.xml');
 goog.require('Blockly.Workspace');
 goog.require('Blockly.Xml');
@@ -47,16 +48,6 @@ Blockly.Procedures.NAME_TYPE = Blockly.PROCEDURE_CATEGORY_NAME;
  */
 Blockly.Procedures.DEFAULT_ARG = 'x';
 
-/**
- * Procedure block type.
- * @typedef {{
- *    getProcedureCall: function():string,
- *    renameProcedure: function(string,string),
- *    getProcedureDef: function():!Array
- * }}
- */
-Blockly.Procedures.ProcedureBlock;
-
 /**
  * Find all user-created procedure definitions in a workspace.
  * @param {!Blockly.Workspace} root Root workspace.