diff --git a/src/SMAPI/Framework/ContentManagers/ModContentManager.cs b/src/SMAPI/Framework/ContentManagers/ModContentManager.cs
index 2c068784..c8a01b70 100644
--- a/src/SMAPI/Framework/ContentManagers/ModContentManager.cs
+++ b/src/SMAPI/Framework/ContentManagers/ModContentManager.cs
@@ -432,6 +432,12 @@ namespace StardewModdingAPI.Framework.ContentManagers
             this.Monitor.VerboseLog($"Fixing tilesheet paths for map '{relativeMapPath}' from mod '{this.ModName}'...");
             foreach (TileSheet tilesheet in map.TileSheets)
             {
+                // validate image source
+                if (string.IsNullOrWhiteSpace(tilesheet.ImageSource))
+                {
+                    throw new SContentLoadException(ContentLoadErrorType.InvalidData, $"Could not load tilesheet '{tilesheet.Id}' for mod {this.ModName} - no image source found.");
+                }
+
                 // get image source
                 tilesheet.ImageSource = this.NormalizePathSeparators(tilesheet.ImageSource);
                 string imageSource = tilesheet.ImageSource;