diff --git a/docs/release-notes.md b/docs/release-notes.md
index 93d07385..903eaf6f 100644
--- a/docs/release-notes.md
+++ b/docs/release-notes.md
@@ -6,6 +6,7 @@
   * Fixed some incompatible-mod errors not showing the mod URL.
   * Fixed rare crash with a specific combination of `manifest.json` fields and internal SMAPI mod data.
   * Fixed update checks not working for Nexus Mods due to a change in their API.
+  * Fixed update checks failing for some older mods with non-standard versions.
 
 * For the [log parser][]:
   * Fixed mod list not including all mods if at least one has no author name.
diff --git a/src/SMAPI.Common/Models/ModSeachModel.cs b/src/SMAPI.Common/Models/ModSeachModel.cs
index 13b05d2d..3c33d0b6 100644
--- a/src/SMAPI.Common/Models/ModSeachModel.cs
+++ b/src/SMAPI.Common/Models/ModSeachModel.cs
@@ -12,6 +12,9 @@ namespace StardewModdingAPI.Common.Models
         /// <summary>The namespaced mod keys to search.</summary>
         public string[] ModKeys { get; set; }
 
+        /// <summary>Whether to allow non-semantic versions, instead of returning an error for those.</summary>
+        public bool AllowInvalidVersions { get; set; }
+
 
         /*********
         ** Public methods
@@ -24,9 +27,11 @@ namespace StardewModdingAPI.Common.Models
 
         /// <summary>Construct an instance.</summary>
         /// <param name="modKeys">The namespaced mod keys to search.</param>
-        public ModSearchModel(IEnumerable<string> modKeys)
+        /// <param name="allowInvalidVersions">Whether to allow non-semantic versions, instead of returning an error for those.</param>
+        public ModSearchModel(IEnumerable<string> modKeys, bool allowInvalidVersions)
         {
             this.ModKeys = modKeys.ToArray();
+            this.AllowInvalidVersions = allowInvalidVersions;
         }
     }
 }
diff --git a/src/SMAPI.Web/Controllers/ModsApiController.cs b/src/SMAPI.Web/Controllers/ModsApiController.cs
index dcb4ec52..abae7db7 100644
--- a/src/SMAPI.Web/Controllers/ModsApiController.cs
+++ b/src/SMAPI.Web/Controllers/ModsApiController.cs
@@ -64,14 +64,15 @@ namespace StardewModdingAPI.Web.Controllers
 
         /// <summary>Fetch version metadata for the given mods.</summary>
         /// <param name="modKeys">The namespaced mod keys to search as a comma-delimited array.</param>
+        /// <param name="allowInvalidVersions">Whether to allow non-semantic versions, instead of returning an error for those.</param>
         [HttpGet]
-        public async Task<IDictionary<string, ModInfoModel>> GetAsync(string modKeys)
+        public async Task<IDictionary<string, ModInfoModel>> GetAsync(string modKeys, bool allowInvalidVersions = false)
         {
             string[] modKeysArray = modKeys?.Split(',').ToArray();
             if (modKeysArray == null || !modKeysArray.Any())
                 return new Dictionary<string, ModInfoModel>();
 
-            return await this.PostAsync(new ModSearchModel(modKeysArray));
+            return await this.PostAsync(new ModSearchModel(modKeysArray, allowInvalidVersions));
         }
 
         /// <summary>Fetch version metadata for the given mods.</summary>
@@ -79,7 +80,8 @@ namespace StardewModdingAPI.Web.Controllers
         [HttpPost]
         public async Task<IDictionary<string, ModInfoModel>> PostAsync([FromBody] ModSearchModel search)
         {
-            // sort & filter keys
+            // parse model
+            bool allowInvalidVersions = search?.AllowInvalidVersions ?? false;
             string[] modKeys = (search?.ModKeys?.ToArray() ?? new string[0])
                 .Distinct(StringComparer.CurrentCultureIgnoreCase)
                 .OrderBy(p => p, StringComparer.CurrentCultureIgnoreCase)
@@ -106,12 +108,20 @@ namespace StardewModdingAPI.Web.Controllers
                 // fetch mod info
                 result[modKey] = await this.Cache.GetOrCreateAsync($"{repository.VendorKey}:{modID}".ToLower(), async entry =>
                 {
-                    entry.AbsoluteExpiration = DateTimeOffset.UtcNow.AddMinutes(this.CacheMinutes);
-
+                    // fetch info
                     ModInfoModel info = await repository.GetModInfoAsync(modID);
-                    if (info.Error == null && (info.Version == null || !Regex.IsMatch(info.Version, this.VersionRegex, RegexOptions.CultureInvariant | RegexOptions.IgnoreCase)))
-                        info = new ModInfoModel(info.Name, info.Version, info.Url, info.Version == null ? "Mod has no version number." : $"Mod has invalid semantic version '{info.Version}'.");
 
+                    // validate
+                    if (info.Error == null)
+                    {
+                        if (info.Version == null)
+                            info = new ModInfoModel(info.Name, info.Version, info.Url, "Mod has no version number.");
+                        if (!allowInvalidVersions && !Regex.IsMatch(info.Version, this.VersionRegex, RegexOptions.CultureInvariant | RegexOptions.IgnoreCase))
+                            info = new ModInfoModel(info.Name, info.Version, info.Url, $"Mod has invalid semantic version '{info.Version}'.");
+                    }
+
+                    // cache & return
+                    entry.AbsoluteExpiration = DateTimeOffset.UtcNow.AddMinutes(this.CacheMinutes);
                     return info;
                 });
             }
diff --git a/src/SMAPI/Framework/ModData/ModDataRecord.cs b/src/SMAPI/Framework/ModData/ModDataRecord.cs
index 79a954f7..56275f53 100644
--- a/src/SMAPI/Framework/ModData/ModDataRecord.cs
+++ b/src/SMAPI/Framework/ModData/ModDataRecord.cs
@@ -106,10 +106,10 @@ namespace StardewModdingAPI.Framework.ModData
 
         /// <summary>Get a semantic local version for update checks.</summary>
         /// <param name="version">The remote version to normalise.</param>
-        public string GetLocalVersionForUpdateChecks(string version)
+        public ISemanticVersion GetLocalVersionForUpdateChecks(ISemanticVersion version)
         {
-            return this.MapLocalVersions != null && this.MapLocalVersions.TryGetValue(version, out string newVersion)
-                ? newVersion
+            return this.MapLocalVersions != null && this.MapLocalVersions.TryGetValue(version.ToString(), out string newVersion)
+                ? new SemanticVersion(newVersion)
                 : version;
         }
 
@@ -117,6 +117,11 @@ namespace StardewModdingAPI.Framework.ModData
         /// <param name="version">The remote version to normalise.</param>
         public string GetRemoteVersionForUpdateChecks(string version)
         {
+            // normalise version if possible
+            if (SemanticVersion.TryParse(version, out ISemanticVersion parsed))
+                version = parsed.ToString();
+
+            // fetch remote version
             return this.MapRemoteVersions != null && this.MapRemoteVersions.TryGetValue(version, out string newVersion)
                 ? newVersion
                 : version;
diff --git a/src/SMAPI/Framework/ModData/ParsedModDataRecord.cs b/src/SMAPI/Framework/ModData/ParsedModDataRecord.cs
index 7f49790d..deb12bdc 100644
--- a/src/SMAPI/Framework/ModData/ParsedModDataRecord.cs
+++ b/src/SMAPI/Framework/ModData/ParsedModDataRecord.cs
@@ -33,7 +33,7 @@ namespace StardewModdingAPI.Framework.ModData
         *********/
         /// <summary>Get a semantic local version for update checks.</summary>
         /// <param name="version">The remote version to normalise.</param>
-        public string GetLocalVersionForUpdateChecks(string version)
+        public ISemanticVersion GetLocalVersionForUpdateChecks(ISemanticVersion version)
         {
             return this.DataRecord.GetLocalVersionForUpdateChecks(version);
         }
diff --git a/src/SMAPI/Framework/WebApiClient.cs b/src/SMAPI/Framework/WebApiClient.cs
index e78ac14b..7f0122cf 100644
--- a/src/SMAPI/Framework/WebApiClient.cs
+++ b/src/SMAPI/Framework/WebApiClient.cs
@@ -40,7 +40,7 @@ namespace StardewModdingAPI.Framework
         {
             return this.Post<ModSearchModel, Dictionary<string, ModInfoModel>>(
                 $"v{this.Version}/mods",
-                new ModSearchModel(modKeys)
+                new ModSearchModel(modKeys, allowInvalidVersions: true)
             );
         }
 
diff --git a/src/SMAPI/Program.cs b/src/SMAPI/Program.cs
index 979f6328..1a1b9645 100644
--- a/src/SMAPI/Program.cs
+++ b/src/SMAPI/Program.cs
@@ -604,29 +604,30 @@ namespace StardewModdingAPI
                         foreach (var result in results)
                         {
                             IModMetadata mod = result.Mod;
-                            ModInfoModel info = result.Info;
+                            ModInfoModel remoteInfo = result.Info;
 
                             // handle error
-                            if (info.Error != null)
+                            if (remoteInfo.Error != null)
                             {
-                                this.Monitor.Log($"   {mod.DisplayName} ({result.Key}): update error: {info.Error}", LogLevel.Trace);
+                                this.Monitor.Log($"   {mod.DisplayName} ({result.Key}): update error: {remoteInfo.Error}", LogLevel.Trace);
                                 continue;
                             }
 
-                            // track update
-                            ISemanticVersion localVersion = mod.DataRecord != null
-                                ? new SemanticVersion(mod.DataRecord.GetLocalVersionForUpdateChecks(mod.Manifest.Version.ToString()))
-                                : mod.Manifest.Version;
-                            ISemanticVersion latestVersion = new SemanticVersion(mod.DataRecord != null
-                                ? mod.DataRecord.GetRemoteVersionForUpdateChecks(new SemanticVersion(info.Version).ToString())
-                                : info.Version
-                            );
-                            bool isUpdate = latestVersion.IsNewerThan(localVersion);
-                            this.VerboseLog($"   {mod.DisplayName} ({result.Key}): {(isUpdate ? $"{mod.Manifest.Version}{(!localVersion.Equals(mod.Manifest.Version) ? $" [{localVersion}]" : "")} => {info.Version}{(!latestVersion.Equals(new SemanticVersion(info.Version)) ? $" [{latestVersion}]" : "")}" : "okay")}.");
+                            // normalise versions
+                            ISemanticVersion localVersion = mod.DataRecord?.GetLocalVersionForUpdateChecks(mod.Manifest.Version) ?? mod.Manifest.Version;
+                            if (!SemanticVersion.TryParse(mod.DataRecord?.GetRemoteVersionForUpdateChecks(remoteInfo.Version) ?? remoteInfo.Version, out ISemanticVersion remoteVersion))
+                            {
+                                this.Monitor.Log($"   {mod.DisplayName} ({result.Key}): update error: Mod has invalid version {remoteInfo.Version}", LogLevel.Trace);
+                                continue;
+                            }
+
+                            // compare versions
+                            bool isUpdate = remoteVersion.IsNewerThan(localVersion);
+                            this.VerboseLog($"   {mod.DisplayName} ({result.Key}): {(isUpdate ? $"{mod.Manifest.Version}{(!localVersion.Equals(mod.Manifest.Version) ? $" [{localVersion}]" : "")} => {remoteInfo.Version}{(!remoteVersion.Equals(new SemanticVersion(remoteInfo.Version)) ? $" [{remoteVersion}]" : "")}" : "okay")}.");
                             if (isUpdate)
                             {
-                                if (!updatesByMod.TryGetValue(mod, out ModInfoModel other) || latestVersion.IsNewerThan(other.Version))
-                                    updatesByMod[mod] = info;
+                                if (!updatesByMod.TryGetValue(mod, out ModInfoModel other) || remoteVersion.IsNewerThan(other.Version))
+                                    updatesByMod[mod] = remoteInfo;
                             }
                         }