diff --git a/doc/errors/index.md b/doc/errors/index.md
index d783685479..687d9efbf1 100644
--- a/doc/errors/index.md
+++ b/doc/errors/index.md
@@ -220,3 +220,11 @@ Duplicate item added to a unique collection.  For example, it may be that you tr
 ### 59
 
 Invalid command found in the PBF.  This indicates that the loaded vector tile may be corrupt.
+
+### 60
+
+Missing or invalid `size`.
+
+### 61
+
+Cannot determine IIIF Image API version from provided image information JSON.
diff --git a/src/ol/format/IIIFInfo.js b/src/ol/format/IIIFInfo.js
index d88db27d22..f6ec81d261 100644
--- a/src/ol/format/IIIFInfo.js
+++ b/src/ol/format/IIIFInfo.js
@@ -89,10 +89,8 @@ function getComplianceLevelOfImageInfoForVersion(imageInfo, version) {
         && typeof imageInfo.profile[0] === 'string') {
         return imageInfo.profile[0];
       }
-      // TODO error: cannot get compliance level URL / string
-      break;
+      return;
     default:
-      // TODO error: invalid Image API version
   }
 }
 
@@ -111,11 +109,10 @@ function getVersionOfImageInfo(imageInfo) {
       if (getComplianceLevelOfImageInfoForVersion(imageInfo, Versions.VERSION1)) {
         return Versions.VERSION1;
       }
-      // TODO error: can't detect Image API version
       break;
     default:
-      // TODO error: can't detect Image API version
   }
+  assert(false, 61);
 }
 
 function getLevelProfileForImageInfo(imageInfo) {
diff --git a/src/ol/source/IIIF.js b/src/ol/source/IIIF.js
index ec49e7a9b7..05babdd608 100644
--- a/src/ol/source/IIIF.js
+++ b/src/ol/source/IIIF.js
@@ -54,9 +54,8 @@ class IIIF extends TileImage {
     const version = options.version || Versions.VERSION2;
     const sizes = options.sizes || [];
     const size = options.size;
-    // TODO Appropriate error code
     assert(size != undefined && Array.isArray(size) && size.length == 2 &&
-      !isNaN(size[0]) && size[0] > 0 && !isNaN(size[1] && size[1] > 0), 999);
+      !isNaN(size[0]) && size[0] > 0 && !isNaN(size[1] && size[1] > 0), 60);
     const width = size[0];
     const height = size[1];
     const tileSize = options.tileSize;