diff --git a/adapters/inmobi/inmobi.go b/adapters/inmobi/inmobi.go
index e12063e781c..a31b93b8c6e 100644
--- a/adapters/inmobi/inmobi.go
+++ b/adapters/inmobi/inmobi.go
@@ -77,7 +77,10 @@ func (a *InMobiAdapter) MakeBids(internalRequest *openrtb2.BidRequest, externalR
 
 	for _, sb := range serverBidResponse.SeatBid {
 		for i := range sb.Bid {
-			mediaType := getMediaTypeForImp(sb.Bid[i])
+			mediaType, err := getMediaTypeForImp(sb.Bid[i])
+			if err != nil {
+				return nil, []error{err}
+			}
 			bidResponse.Bids = append(bidResponse.Bids, &adapters.TypedBid{
 				Bid:     &sb.Bid[i],
 				BidType: mediaType,
@@ -118,17 +121,19 @@ func preprocess(imp *openrtb2.Imp) error {
 	return nil
 }
 
-func getMediaTypeForImp(bid openrtb2.Bid) openrtb_ext.BidType {
+func getMediaTypeForImp(bid openrtb2.Bid) (openrtb_ext.BidType, error) {
 	switch bid.MType {
 	case openrtb2.MarkupBanner:
-		return openrtb_ext.BidTypeBanner
+		return openrtb_ext.BidTypeBanner, nil
 	case openrtb2.MarkupVideo:
-		return openrtb_ext.BidTypeVideo
+		return openrtb_ext.BidTypeVideo, nil
 	case openrtb2.MarkupAudio:
-		return openrtb_ext.BidTypeAudio
+		return openrtb_ext.BidTypeAudio, nil
 	case openrtb2.MarkupNative:
-		return openrtb_ext.BidTypeNative
+		return openrtb_ext.BidTypeNative, nil
 	default:
-		return openrtb_ext.BidTypeBanner
+		return "", &errortypes.BadServerResponse{
+			Message: fmt.Sprintf("Unsupported mtype %d for bid %s", bid.MType, bid.ID),
+		}
 	}
 }
diff --git a/adapters/inmobi/inmobitest/supplemental/invalid-mtype.json b/adapters/inmobi/inmobitest/supplemental/invalid-mtype.json
new file mode 100644
index 00000000000..af2192836b0
--- /dev/null
+++ b/adapters/inmobi/inmobitest/supplemental/invalid-mtype.json
@@ -0,0 +1,97 @@
+{
+  "mockBidRequest": {
+    "site": {
+      "page": "https://www.inmobi.com"
+    },
+    "id": "req-id",
+    "device": {
+      "ip": "1.1.1.1",
+      "ua": "Mozilla/5.0 (Linux; Android 8.0.0; SM-G960F Build/R16NW) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/62.0.3202.84 Mobile Safari/537.36"
+    },
+    "imp": [
+      {
+        "ext": {
+          "bidder": {
+            "plc": "1621323101291"
+          }
+        },
+        "video": {
+          "w": 640,
+          "h": 360,
+          "mimes": ["video/mp4"]
+        },
+        "id": "imp-id"
+      }
+    ]
+  },
+  "httpCalls": [{
+    "expectedRequest": {
+      "uri": "https://api.w.inmobi.com/showad/openrtb/bidder/prebid",
+      "body": {
+        "site": {
+          "page": "https://www.inmobi.com"
+        },
+        "id": "req-id",
+        "device": {
+          "ip": "1.1.1.1",
+          "ua": "Mozilla/5.0 (Linux; Android 8.0.0; SM-G960F Build/R16NW) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/62.0.3202.84 Mobile Safari/537.36"
+        },
+        "imp": [
+          {
+            "ext": {
+              "bidder": {
+                "plc": "1621323101291"
+              }
+            },
+            "video": {
+              "w": 640,
+              "h": 360,
+              "mimes": ["video/mp4"]
+            },
+            "id": "imp-id"
+          }
+        ]
+      },
+      "impIDs":["imp-id"]
+    },
+    "mockResponse": {
+      "status": 200,
+      "body": {
+        "id": "req-id",
+        "seatbid": [
+          {
+            "bid": [
+              {
+                "ext": {
+                  "prebid": {
+                    "meta": {
+                      "networkName": "inmobi"
+                    }
+                  }
+                },
+                "nurl": "https://some.event.url/params",
+                "crid": "123456789",
+                "adomain": [],
+                "price": 2.0,
+                "id": "1234",
+                "adm": "<?xml version=\"1.0\" encoding=\"UTF-8\"?> <VAST version=\"3.0\"></VAST>",
+                "impid": "imp-id",
+                "mtype": 0
+              }
+            ]
+          }
+        ]
+      }
+    }
+  }],
+
+  "expectedBidResponses":[],
+  "expectedMakeBidsErrors":[
+    {
+      "value":"Unsupported mtype 0 for bid 1234",
+      "comparison":"literal"
+    }
+  ]
+}
+
+