diff --git a/docs/release-notes.md b/docs/release-notes.md
index 0f6fba33..aa9b488c 100644
--- a/docs/release-notes.md
+++ b/docs/release-notes.md
@@ -4,7 +4,8 @@
 ## Upcoming version
 * For players:
   * You no longer need .NET 5 installed to run SMAPI or the installer.
-  * Updated for the Stardew Valley 1.5.5 hotfix on 2021-12-03.
+  * The installer now detects when the game folder contains an incompatible older game version.
+  * Updated for the latest Stardew Valley 1.5.5 hotfix.
 
 * For SMAPI maintainers:
   * Added a new [scripted release package process](technical/smapi.md), which removes the need to compile SMAPI on multiple platforms and manually combine them.
diff --git a/src/SMAPI.Installer/Framework/InstallerContext.cs b/src/SMAPI.Installer/Framework/InstallerContext.cs
index 95df32ca..68df2001 100644
--- a/src/SMAPI.Installer/Framework/InstallerContext.cs
+++ b/src/SMAPI.Installer/Framework/InstallerContext.cs
@@ -54,5 +54,12 @@ namespace StardewModdingAPI.Installer.Framework
         {
             return this.GameScanner.LooksLikeGameFolder(dir);
         }
+
+        /// <summary>Get whether a folder seems to contain Stardew Valley 1.5.4 or earlier.</summary>
+        /// <param name="dir">The folder to check.</param>
+        public bool LooksLikeStardewValley154(DirectoryInfo dir)
+        {
+            return this.GameScanner.LooksLikeStardewValley154(dir);
+        }
     }
 }
diff --git a/src/SMAPI.Installer/InteractiveInstaller.cs b/src/SMAPI.Installer/InteractiveInstaller.cs
index d8c27a2d..424fe42b 100644
--- a/src/SMAPI.Installer/InteractiveInstaller.cs
+++ b/src/SMAPI.Installer/InteractiveInstaller.cs
@@ -704,7 +704,15 @@ namespace StardewModdingApi.Installer
                 }
                 if (!context.LooksLikeGameFolder(directory))
                 {
-                    this.PrintWarning("That directory doesn't contain a Stardew Valley executable.");
+                    if (context.LooksLikeStardewValley154(directory))
+                    {
+                        this.PrintWarning("That directory seems to have Stardew Valley 1.5.4 or earlier.");
+                        this.PrintWarning("Please update your game to the latest version to use SMAPI.");
+                    }
+                    else
+                    {
+                        this.PrintWarning("That directory doesn't contain a Stardew Valley executable.");
+                    }
                     continue;
                 }
 
diff --git a/src/SMAPI.Toolkit/Framework/GameScanning/GameScanner.cs b/src/SMAPI.Toolkit/Framework/GameScanning/GameScanner.cs
index 7553c07f..c7ebe6e0 100644
--- a/src/SMAPI.Toolkit/Framework/GameScanning/GameScanner.cs
+++ b/src/SMAPI.Toolkit/Framework/GameScanning/GameScanner.cs
@@ -5,6 +5,7 @@ using System.Linq;
 using System.Xml.Linq;
 using System.Xml.XPath;
 using StardewModdingAPI.Toolkit.Utilities;
+using System.Reflection;
 #if SMAPI_FOR_WINDOWS
 using Microsoft.Win32;
 #endif
@@ -59,6 +60,32 @@ namespace StardewModdingAPI.Toolkit.Framework.GameScanning
                 && dir.EnumerateFiles("Stardew Valley.dll").Any();
         }
 
+        /// <summary>Get whether a folder seems to contain Stardew Valley 1.5.4 or earlier.</summary>
+        /// <param name="dir">The folder to check.</param>
+        public bool LooksLikeStardewValley154(DirectoryInfo dir)
+        {
+            if (!dir.Exists || this.LooksLikeGameFolder(dir))
+                return false;
+
+            // get legacy executable
+            FileInfo executable = new FileInfo(Path.Combine(dir.FullName, "Stardew Valley.exe"));
+            if (!executable.Exists)
+                executable = new FileInfo(Path.Combine(dir.FullName, "StardewValley.exe"));
+            if (!executable.Exists)
+                return false;
+
+            // check if it's a standard .NET assembly
+            // This will fail in Stardew Valley 1.5.5+, where it's a binary wrapper around Stardew Valley.dll.
+            try
+            {
+                Version version = AssemblyName.GetAssemblyName(executable.FullName).Version;
+                return true;
+            }
+            catch
+            {
+                return false;
+            }
+        }
 
         /*********
         ** Private methods