diff --git a/endpoints/openrtb2/amp_auction.go b/endpoints/openrtb2/amp_auction.go
index 586481ddfc5..2dcd572c63c 100644
--- a/endpoints/openrtb2/amp_auction.go
+++ b/endpoints/openrtb2/amp_auction.go
@@ -407,31 +407,34 @@ func (deps *endpointDeps) overrideWithParams(httpRequest *http.Request, req *ope
 }
 
 func makeFormatReplacement(overrideWidth uint64, overrideHeight uint64, width uint64, height uint64, multisize string) []openrtb.Format {
+	var formats []openrtb.Format
 	if overrideWidth != 0 && overrideHeight != 0 {
-		return []openrtb.Format{{
+		formats = []openrtb.Format{{
 			W: overrideWidth,
 			H: overrideHeight,
 		}}
 	} else if overrideWidth != 0 && height != 0 {
-		return []openrtb.Format{{
+		formats = []openrtb.Format{{
 			W: overrideWidth,
 			H: height,
 		}}
 	} else if width != 0 && overrideHeight != 0 {
-		return []openrtb.Format{{
+		formats = []openrtb.Format{{
 			W: width,
 			H: overrideHeight,
 		}}
-	} else if parsedSizes := parseMultisize(multisize); len(parsedSizes) != 0 {
-		return parsedSizes
 	} else if width != 0 && height != 0 {
-		return []openrtb.Format{{
+		formats = []openrtb.Format{{
 			W: width,
 			H: height,
 		}}
 	}
 
-	return nil
+	if parsedSizes := parseMultisize(multisize); len(parsedSizes) != 0 {
+		formats = append(formats, parsedSizes...)
+	}
+
+	return formats
 }
 
 func setWidths(formats []openrtb.Format, width uint64) {
diff --git a/endpoints/openrtb2/amp_auction_test.go b/endpoints/openrtb2/amp_auction_test.go
index 289db3f48cb..731fd55e196 100644
--- a/endpoints/openrtb2/amp_auction_test.go
+++ b/endpoints/openrtb2/amp_auction_test.go
@@ -832,6 +832,24 @@ func TestMultisize(t *testing.T) {
 	}.execute(t)
 }
 
+func TestSizeWithMultisize(t *testing.T) {
+	formatOverrideSpec{
+		width:     20,
+		height:    40,
+		multisize: "200x50,100x60",
+		expect: []openrtb.Format{{
+			W: 20,
+			H: 40,
+		}, {
+			W: 200,
+			H: 50,
+		}, {
+			W: 100,
+			H: 60,
+		}},
+	}.execute(t)
+}
+
 func TestHeightOnly(t *testing.T) {
 	formatOverrideSpec{
 		height: 200,