diff --git a/__tests__/modify-master-external-image.test.ts b/__tests__/modify-master-external-image.test.ts
new file mode 100644
index 0000000..5746636
--- /dev/null
+++ b/__tests__/modify-master-external-image.test.ts
@@ -0,0 +1,29 @@
+import Automizer from '../src/automizer';
+import { ModifyImageHelper, ModifyShapeHelper } from '../src';
+import { CmToDxa } from '../src/helper/modify-helper';
+
+test('Load external media, modify image target on slide master', async () => {
+  const automizer = new Automizer({
+    templateDir: `${__dirname}/../__tests__/pptx-templates`,
+    outputDir: `${__dirname}/../__tests__/pptx-output`,
+    mediaDir: `${__dirname}/../__tests__/images`,
+    removeExistingSlides: true,
+    cleanup: true,
+  });
+
+  const pres = automizer
+    .loadRoot(`RootTemplateWithImages.pptx`)
+    .loadMedia([`test.jpg`])
+    .load(`RootTemplateWithImages.pptx`, 'base');
+
+  pres.addMaster('base', 1, (master) => {
+    master.modifyElement('masterImagePNG', [
+      ModifyImageHelper.setRelationTarget('test.jpg'),
+    ]);
+  });
+
+  // Expect imported slide master (#2) to have swapped (left top) background image
+  const result = await pres.write(`modify-master-add-external-image.test.pptx`);
+
+  expect(result.images).toBe(8);
+});
diff --git a/__tests__/pptx-templates/RootTemplateWithImages.pptx b/__tests__/pptx-templates/RootTemplateWithImages.pptx
index 1d9e0bb..9c1bacd 100644
Binary files a/__tests__/pptx-templates/RootTemplateWithImages.pptx and b/__tests__/pptx-templates/RootTemplateWithImages.pptx differ
diff --git a/src/classes/has-shapes.ts b/src/classes/has-shapes.ts
index 5d7bd2c..38c1be1 100644
--- a/src/classes/has-shapes.ts
+++ b/src/classes/has-shapes.ts
@@ -32,6 +32,7 @@ import { Image } from '../shapes/image';
 import { ElementType } from '../enums/element-type';
 import { GenericShape } from '../shapes/generic';
 import { XmlSlideHelper } from '../helper/xml-slide-helper';
+import { vd } from '../helper/general-helper';
 
 export default class HasShapes {
   /**
@@ -387,17 +388,27 @@ export default class HasShapes {
         ? this.getSlideNumber(template, importElement.slideNumber)
         : importElement.slideNumber;
 
-    let sourcePath = `ppt/slides/slide${slideNumber}.xml`;
-
+    let currentMode = 'slideToSlide';
     if (this.targetType === 'slideMaster') {
-      // It is possible to import shapes from loaded presentations,
-      // as well as to modify an existing shape on current slideMaster
-      sourcePath =
-        importElement.mode === 'append'
-          ? `ppt/slides/slide${slideNumber}.xml`
-          : `ppt/slideMasters/slideMaster${slideNumber}.xml`;
+      if (importElement.mode === 'append') {
+        currentMode = 'slideToMaster';
+      } else {
+        currentMode = 'onMaster';
+      }
     }
 
+    // It is possible to import shapes from loaded slides to slideMaster,
+    // as well as to modify an existing shape on current slideMaster
+    const sourcePath =
+      currentMode === 'onMaster'
+        ? `ppt/slideMasters/slideMaster${slideNumber}.xml`
+        : `ppt/slides/slide${slideNumber}.xml`;
+
+    const sourceRelPath =
+      currentMode === 'onMaster'
+        ? `ppt/slideMasters/_rels/slideMaster${slideNumber}.xml.rels`
+        : `ppt/slides/_rels/slide${slideNumber}.xml.rels`;
+
     const sourceArchive = await template.archive;
     const useCreationIds =
       template.useCreationIds === true && template.creationIds !== undefined;
@@ -420,7 +431,7 @@ export default class HasShapes {
     const appendElementParams = await this.analyzeElement(
       sourceElement,
       sourceArchive,
-      slideNumber,
+      sourceRelPath,
     );
 
     return {
@@ -754,13 +765,13 @@ export default class HasShapes {
   async analyzeElement(
     sourceElement: XmlElement,
     sourceArchive: IArchive,
-    slideNumber: number,
+    relsPath: string,
   ): Promise<AnalyzedElementType> {
     const isChart = sourceElement.getElementsByTagName('c:chart');
     if (isChart.length) {
       const target = await XmlHelper.getTargetByRelId(
         sourceArchive,
-        slideNumber,
+        relsPath,
         sourceElement,
         'chart',
       );
@@ -775,7 +786,7 @@ export default class HasShapes {
     if (isChartEx.length) {
       const target = await XmlHelper.getTargetByRelId(
         sourceArchive,
-        slideNumber,
+        relsPath,
         sourceElement,
         'chartEx',
       );
@@ -792,7 +803,7 @@ export default class HasShapes {
         type: ElementType.Image,
         target: await XmlHelper.getTargetByRelId(
           sourceArchive,
-          slideNumber,
+          relsPath,
           sourceElement,
           'image',
         ),
diff --git a/src/helper/xml-helper.ts b/src/helper/xml-helper.ts
index d45e275..310a57e 100644
--- a/src/helper/xml-helper.ts
+++ b/src/helper/xml-helper.ts
@@ -331,7 +331,7 @@ export class XmlHelper {
 
   static async getTargetByRelId(
     archive: IArchive,
-    slideNumber: number,
+    relsPath: string,
     element: XmlElement,
     type: string,
   ): Promise<Target> {
@@ -339,7 +339,6 @@ export class XmlHelper {
     const sourceRid = element
       .getElementsByTagName(params.relRootTag)[0]
       .getAttribute(params.relAttribute);
-    const relsPath = `ppt/slides/_rels/slide${slideNumber}.xml.rels`;
     const imageRels = await XmlHelper.getRelationshipTargetsByPrefix(
       archive,
       relsPath,
diff --git a/src/shapes/image.ts b/src/shapes/image.ts
index 49d11d7..b5f6380 100644
--- a/src/shapes/image.ts
+++ b/src/shapes/image.ts
@@ -82,9 +82,10 @@ export class Image extends Shape implements IImage {
     this.applyImageCallbacks();
 
     if (this.hasSvgRelation()) {
+      const relsPath = `ppt/slides/_rels/slide${this.sourceSlideNumber}.xml.rels`;
       const target = await XmlHelper.getTargetByRelId(
         this.sourceArchive,
-        this.sourceSlideNumber,
+        relsPath,
         this.targetElement,
         'image:svg',
       );