diff --git a/src/components/prompt/prompt.jsx b/src/components/prompt/prompt.jsx
index 1d648448140..2fd19b58570 100644
--- a/src/components/prompt/prompt.jsx
+++ b/src/components/prompt/prompt.jsx
@@ -40,7 +40,41 @@ const messages = defineMessages({
     }
 });
 
-const PromptComponent = props => (
+const PromptComponent = props => props.isCustom ? (
+    <Modal
+        className={styles.modalContent}
+        contentLabel={props.title}
+        id="customModal"
+        onRequestClose={props.onCancel}
+    >
+        <Box className={styles.body}>
+            <Box>
+            </Box>
+            <Box className={styles.buttonRow}>
+                <button
+                    className={styles.cancelButton}
+                    onClick={props.onCancel}
+                >
+                    <FormattedMessage
+                        defaultMessage={props.closeTitle}
+                        description="Button in prompt for cancelling the dialog"
+                        id="gui.prompt.cancel"
+                    />
+                </button>
+                <button
+                    className={styles.okButton}
+                    onClick={props.onOk}
+                >
+                    <FormattedMessage
+                        defaultMessage={props.enterTitle}
+                        description="Button in prompt for confirming the dialog"
+                        id="gui.prompt.ok"
+                    />
+                </button>
+            </Box>
+        </Box>
+    </Modal>
+) : (
     <Modal
         className={styles.modalContent}
         contentLabel={props.title}
@@ -188,24 +222,29 @@ const PromptComponent = props => (
 );
 
 PromptComponent.propTypes = {
-    isAddingCloudVariableScratchSafe: PropTypes.bool.isRequired,
-    canAddCloudVariable: PropTypes.bool.isRequired,
-    cloudSelected: PropTypes.bool.isRequired,
-    defaultValue: PropTypes.string,
-    globalSelected: PropTypes.bool.isRequired,
-    isStage: PropTypes.bool.isRequired,
-    showListMessage: PropTypes.bool.isRequired,
-    label: PropTypes.string.isRequired,
+    title: PropTypes.string.isRequired,
     onCancel: PropTypes.func.isRequired,
-    onChange: PropTypes.func.isRequired,
-    onCloudVarOptionChange: PropTypes.func,
-    onFocus: PropTypes.func.isRequired,
     onKeyPress: PropTypes.func.isRequired,
     onOk: PropTypes.func.isRequired,
-    onScopeOptionSelection: PropTypes.func.isRequired,
-    showCloudOption: PropTypes.bool.isRequired,
-    showVariableOptions: PropTypes.bool.isRequired,
-    title: PropTypes.string.isRequired
+    isAddingCloudVariableScratchSafe: PropTypes.bool,
+    canAddCloudVariable: PropTypes.bool,
+    cloudSelected: PropTypes.bool,
+    defaultValue: PropTypes.string,
+    globalSelected: PropTypes.bool,
+    isStage: PropTypes.bool,
+    showListMessage: PropTypes.bool,
+    label: PropTypes.string,
+    onChange: PropTypes.func,
+    onCloudVarOptionChange: PropTypes.func,
+    onFocus: PropTypes.func,
+    onScopeOptionSelection: PropTypes.func,
+    showCloudOption: PropTypes.bool,
+    showVariableOptions: PropTypes.bool,
+
+    /* custom modals */
+    isCustom: PropTypes.bool,
+    enterTitle: PropTypes.string,
+    closeTitle: PropTypes.string
 };
 
 export default PromptComponent;
diff --git a/src/containers/blocks.jsx b/src/containers/blocks.jsx
index 807fa98977f..43c2eeebdca 100644
--- a/src/containers/blocks.jsx
+++ b/src/containers/blocks.jsx
@@ -137,6 +137,7 @@ class Blocks extends React.Component {
             'handleEnableProcedureReturns'
         ]);
         this.ScratchBlocks.prompt = this.handlePromptStart;
+        this.ScratchBlocks.customPrompt = this.handleCustomPrompt;
         this.ScratchBlocks.statusButtonCallback = this.handleConnectionModalStart;
         this.ScratchBlocks.recordSoundCallback = this.handleOpenSoundRecorder;
 
@@ -609,6 +610,47 @@ class Blocks extends React.Component {
         p.prompt.showCloudOption = (optVarType === this.ScratchBlocks.SCALAR_VARIABLE_TYPE) && this.props.canUseCloud;
         this.setState(p);
     }
+    handleCustomPrompt (title, scale, enterInfo, closeInfo) {
+        const isObject = (value) => typeof value === 'object' && !Array.isArray(value);
+        let needsExit = false;
+        const exitFunc = (message) => {
+            needsExit = true;
+            console.error(message);
+        };
+
+        /* validate arguments */
+        if (isObject(scale)) {
+            if (!scale.width || !scale.height) exitFunc("Custom Modal -- Missing width/height number property in Param 2");
+        } else {
+            exitFunc("Custom Modal -- Param 2 must be a object with 'width' and 'height' number properties");
+        }
+        if (isObject(enterInfo)) {
+            if (!scale.name || !scale.callback) exitFunc("Custom Modal -- Missing width/height number property in Param 3");
+            if (scale.callback && typeof scale.callback !== 'function') exitFunc("Custom Modal -- callback property in Param 3 must be a function");
+        } else {
+            exitFunc("Custom Modal -- Param 3 must be a object with properties: 'name' (string) and 'callback' (function)");
+        }
+        if (isObject(closeInfo)) {
+            if (!scale.name || !scale.callback) exitFunc("Custom Modal -- Missing width/height number property in Param 4");
+            if (scale.callback && typeof scale.callback !== 'function') exitFunc("Custom Modal -- callback property in Param 4 must be a function");
+        } else {
+            exitFunc("Custom Modal -- Param 4 must be a object with properties: 'name' (string) and 'callback' (function)");
+        }
+        if (needsExit) return;
+
+        this.setState({prompt: {
+            isCustom: true,
+            title, enterInfo, closeInfo
+        }});
+
+        const modal = document.querySelector(`div[class="ReactModalPortal"]`);
+        if (modal) {
+            const inner = modal.firstChild.firstChild;
+            inner.style.width = `${scale.width}px`;
+            inner.style.height = `${scale.height}px`;
+            return inner.querySelector(`div[class*="prompt_body_"] div`);
+        }
+    }
     handleConnectionModalStart (extensionId) {
         this.props.onOpenConnectionModal(extensionId);
     }
@@ -625,6 +667,11 @@ class Blocks extends React.Component {
      * to the variable validation prompt callback used in scratch-blocks.
      */
     handlePromptCallback (input, variableOptions) {
+        if (this.state.prompt.isCustom) {
+            this.state.prompt.enterInfo.callback();
+            this.setState({prompt: null});
+            return;
+        }
         this.state.prompt.callback(
             input,
             this.props.vm.runtime.getAllVarNamesOfType(this.state.prompt.varType),
@@ -632,6 +679,7 @@ class Blocks extends React.Component {
         this.handlePromptClose();
     }
     handlePromptClose () {
+        if (this.state.prompt.isCustom) this.state.prompt.closeInfo.callback();
         this.setState({prompt: null});
     }
     handleCustomProceduresClose (data) {
@@ -687,7 +735,17 @@ class Blocks extends React.Component {
                     onDrop={this.handleDrop}
                     {...props}
                 />
-                {this.state.prompt ? (
+                {this.state.prompt ? this.state.prompt.isCustom ? (
+                    <Prompt
+                        isCustom={this.state.prompt.isCustom}
+                        title={this.state.prompt.title}
+                        enterTitle={this.state.prompt.enterInfo.name}
+                        closeTitle={this.state.prompt.closeInfo.name}
+                        vm={vm}
+                        onCancel={this.handlePromptClose}
+                        onOk={this.handlePromptCallback}
+                    />
+                ) : (
                     <Prompt
                         defaultValue={this.state.prompt.defaultValue}
                         isStage={vm.runtime.getEditingTarget().isStage}
diff --git a/src/containers/prompt.jsx b/src/containers/prompt.jsx
index 011e00e2e54..0a279338360 100644
--- a/src/containers/prompt.jsx
+++ b/src/containers/prompt.jsx
@@ -34,7 +34,8 @@ class Prompt extends React.Component {
         event.target.select();
     }
     handleOk () {
-        this.props.onOk(this.state.inputValue, {
+        if (this.props.isCustom) this.props.onOk();
+        else this.props.onOk(this.state.inputValue, {
             scope: this.state.globalSelected ? 'global' : 'local',
             isCloud: this.state.cloudSelected
         });
@@ -58,7 +59,18 @@ class Prompt extends React.Component {
         }
     }
     render () {
-        return (
+        if (this.props.isCustom) return (
+            <PromptComponent
+                isCustom={this.props.isCustom}
+                title={this.props.title}
+                enterTitle={this.props.enterTitle}
+                closeTitle={this.props.closeTitle}
+                onOk={this.handleOk}
+                onCancel={this.handleCancel}
+                onKeyPress={this.handleKeyPress}
+            />
+        )
+        else return (
             <PromptComponent
                 isAddingCloudVariableScratchSafe={this.state.isAddingCloudVariableScratchSafe}
                 canAddCloudVariable={this.state.canAddCloudVariable}
@@ -84,16 +96,21 @@ class Prompt extends React.Component {
 }
 
 Prompt.propTypes = {
-    defaultValue: PropTypes.string,
-    isStage: PropTypes.bool.isRequired,
-    showListMessage: PropTypes.bool.isRequired,
-    label: PropTypes.string.isRequired,
+    title: PropTypes.string.isRequired,
     onCancel: PropTypes.func.isRequired,
     onOk: PropTypes.func.isRequired,
-    showCloudOption: PropTypes.bool.isRequired,
-    showVariableOptions: PropTypes.bool.isRequired,
-    title: PropTypes.string.isRequired,
-    vm: PropTypes.instanceOf(VM)
+    defaultValue: PropTypes.string,
+    isStage: PropTypes.bool,
+    showListMessage: PropTypes.bool,
+    label: PropTypes.string,
+    showCloudOption: PropTypes.bool,
+    showVariableOptions: PropTypes.bool,
+    vm: PropTypes.instanceOf(VM),
+
+    /* custom modals */
+    isCustom: PropTypes.bool,
+    enterTitle: PropTypes.string,
+    closeTitle: PropTypes.string
 };
 
 export default Prompt;