diff --git a/blocks/procedures.ts b/blocks/procedures.ts
index 7f4a0ef5c..25fe240b8 100644
--- a/blocks/procedures.ts
+++ b/blocks/procedures.ts
@@ -921,10 +921,9 @@ const PROCEDURE_CALL_COMMON = {
           type: 'field_label',
           text: this.arguments_[i],
         }) as FieldLabel;
-        const input = this.appendValueInput('ARG' + i)
+        this.appendValueInput('ARG' + i)
           .setAlign(Align.RIGHT)
           .appendField(newField, 'ARGNAME' + i);
-        input.init();
       }
     }
     // Remove deleted inputs.
@@ -937,7 +936,6 @@ const PROCEDURE_CALL_COMMON = {
       if (this.arguments_.length) {
         if (!this.getField('WITH')) {
           topRow.appendField(Msg['PROCEDURES_CALL_BEFORE_PARAMS'], 'WITH');
-          topRow.init();
         }
       } else {
         if (this.getField('WITH')) {
diff --git a/core/block.ts b/core/block.ts
index becc8c91b..ea7b63a7a 100644
--- a/core/block.ts
+++ b/core/block.ts
@@ -191,6 +191,13 @@ export class Block implements IASTNodeLocation, IDeletable {
    */
   private disposing = false;
 
+  /**
+   * Has this block been fully initialized? E.g. all fields initailized.
+   *
+   * @internal
+   */
+  initialized = false;
+
   private readonly xy_: Coordinate;
   isInFlyout: boolean;
   isInMutator: boolean;
@@ -373,13 +380,11 @@ export class Block implements IASTNodeLocation, IDeletable {
    * change).
    */
   initModel() {
+    if (this.initialized) return;
     for (const input of this.inputList) {
-      for (const field of input.fieldRow) {
-        if (field.initModel) {
-          field.initModel();
-        }
-      }
+      input.initModel();
     }
+    this.initialized = true;
   }
 
   /**
diff --git a/core/block_svg.ts b/core/block_svg.ts
index 5dcb1d4bd..d9f61dd6d 100644
--- a/core/block_svg.ts
+++ b/core/block_svg.ts
@@ -163,6 +163,9 @@ export class BlockSvg
    */
   constructor(workspace: WorkspaceSvg, prototypeName: string, opt_id?: string) {
     super(workspace, prototypeName, opt_id);
+    if (!workspace.rendered) {
+      throw TypeError('Cannot create a rendered block in a headless workspace');
+    }
     this.workspace = workspace;
     this.svgGroup_ = dom.createSvgElement(Svg.G, {});
 
@@ -189,10 +192,8 @@ export class BlockSvg
    * May be called more than once.
    */
   initSvg() {
-    if (!this.workspace.rendered) {
-      throw TypeError('Workspace is headless.');
-    }
-    for (let i = 0, input; (input = this.inputList[i]); i++) {
+    if (this.initialized) return;
+    for (const input of this.inputList) {
       input.init();
     }
     for (const icon of this.getIcons()) {
@@ -202,7 +203,7 @@ export class BlockSvg
     this.applyColour();
     this.pathObject.updateMovable(this.isMovable());
     const svg = this.getSvgRoot();
-    if (!this.workspace.options.readOnly && !this.eventsInit_ && svg) {
+    if (!this.workspace.options.readOnly && svg) {
       browserEvents.conditionalBind(
         svg,
         'pointerdown',
@@ -210,11 +211,11 @@ export class BlockSvg
         this.onMouseDown_,
       );
     }
-    this.eventsInit_ = true;
 
     if (!svg.parentNode) {
       this.workspace.getCanvas().appendChild(svg);
     }
+    this.initialized = true;
   }
 
   /**
diff --git a/core/field.ts b/core/field.ts
index 4ee4b1763..0a22797bf 100644
--- a/core/field.ts
+++ b/core/field.ts
@@ -314,6 +314,7 @@ export abstract class Field<T = any>
     this.setTooltip(this.tooltip_);
     this.bindEvents_();
     this.initModel();
+    this.applyColour();
   }
 
   /**
diff --git a/core/inputs/input.ts b/core/inputs/input.ts
index bcf8cab78..da7cccad5 100644
--- a/core/inputs/input.ts
+++ b/core/inputs/input.ts
@@ -103,10 +103,7 @@ export class Input {
     }
 
     field.setSourceBlock(this.sourceBlock);
-    if (this.sourceBlock.rendered) {
-      field.init();
-      field.applyColour();
-    }
+    if (this.sourceBlock.initialized) this.initField(field);
     field.name = opt_name;
     field.setVisible(this.isVisible());
 
@@ -270,11 +267,28 @@ export class Input {
 
   /** Initialize the fields on this input. */
   init() {
-    if (!this.sourceBlock.rendered) {
-      return; // Headless blocks don't need fields initialized.
+    for (const field of this.fieldRow) {
+      field.init();
     }
-    for (let i = 0; i < this.fieldRow.length; i++) {
-      this.fieldRow[i].init();
+  }
+
+  /**
+   * Initializes the fields on this input for a headless block.
+   *
+   * @internal
+   */
+  public initModel() {
+    for (const field of this.fieldRow) {
+      field.initModel();
+    }
+  }
+
+  /** Initializes the given field. */
+  private initField(field: Field) {
+    if (this.sourceBlock.rendered) {
+      field.init();
+    } else {
+      field.initModel();
     }
   }
 
diff --git a/core/render_management.ts b/core/render_management.ts
index 5aadc563c..c5e3d2af5 100644
--- a/core/render_management.ts
+++ b/core/render_management.ts
@@ -166,6 +166,7 @@ function shouldRenderRootBlock(block: BlockSvg): boolean {
  */
 function renderBlock(block: BlockSvg) {
   if (!dirtyBlocks.has(block)) return;
+  if (!block.initialized) return;
   for (const child of block.getChildren(false)) {
     renderBlock(child);
   }
diff --git a/tests/mocha/render_management_test.js b/tests/mocha/render_management_test.js
index 971ed1667..9d368ef7b 100644
--- a/tests/mocha/render_management_test.js
+++ b/tests/mocha/render_management_test.js
@@ -33,6 +33,7 @@ suite('Render Management', function () {
         getRelativeToSurfaceXY: () => ({x: 0, y: 0}),
         updateComponentLocations: () => {},
         bumpNeighbours: () => {},
+        initialized: true,
         workspace: {
           resizeContents: () => {},
         },