diff --git a/src/ChibiRuby.Cli/Program.cs b/src/ChibiRuby.Cli/Program.cs
index 67312ba..9187ab5 100644
--- a/src/ChibiRuby.Cli/Program.cs
+++ b/src/ChibiRuby.Cli/Program.cs
@@ -31,47 +31,59 @@ public void Compile(
         var state = MRubyState.Create();
         var inputBytes = File.ReadAllBytes(inputFile);
 
-        if (dump)
+        try
         {
-            Irep irep;
-            if (IsBytecode(inputFile, inputBytes))
+            if (dump)
             {
-                irep = state.ParseBytecode(inputBytes);
+                Irep irep;
+                if (IsBytecode(inputFile, inputBytes))
+                {
+                    irep = state.ParseBytecode(inputBytes);
+                }
+                else
+                {
+                    var compiler = MRubyCompiler.Create(state);
+                    using var compilation = compiler.Compile(inputBytes);
+                    irep = state.ParseBytecode(compilation.AsBytecode());
+                }
+
+                var bufferWriter = new ArrayBufferWriter<byte>();
+                DumpIrepRecursive(state, irep, bufferWriter);
+
+                using var outputStream = output is null or "-"
+                    ? Console.OpenStandardOutput()
+                    : File.Create(output);
+                outputStream.Write(bufferWriter.WrittenSpan);
             }
             else
             {
                 var compiler = MRubyCompiler.Create(state);
                 using var compilation = compiler.Compile(inputBytes);
-                irep = state.ParseBytecode(compilation.AsBytecode());
-            }
 
-            var bufferWriter = new ArrayBufferWriter<byte>();
-            DumpIrepRecursive(state, irep, bufferWriter);
+                // Resolve the bytecode before opening the destination so a compile error
+                // doesn't leave behind a truncated/empty output file.
+                var bytecode = compilation.AsBytecode().ToArray();
 
-            using var outputStream = output is null or "-"
-                ? Console.OpenStandardOutput()
-                : File.Create(output);
-            outputStream.Write(bufferWriter.WrittenSpan);
-        }
-        else
-        {
-            var compiler = MRubyCompiler.Create(state);
-            using var compilation = compiler.Compile(inputBytes);
+                using var outputStream = output == "-"
+                    ? Console.OpenStandardOutput()
+                    : File.Create(output ?? GetDefaultOutputPath(inputFile, format));
 
-            using var outputStream = output == "-"
-                ? Console.OpenStandardOutput()
-                : File.Create(output ?? GetDefaultOutputPath(inputFile, format));
-
-            switch (format)
-            {
-                case OutputFormat.binary:
-                    outputStream.Write(compilation.AsBytecode());
-                    break;
-                case OutputFormat.csharp:
-                    WriteCSharpOutput(outputStream, compilation.AsBytecode(), csharpNamespace, csharpClassName);
-                    break;
+                switch (format)
+                {
+                    case OutputFormat.binary:
+                        outputStream.Write(bytecode);
+                        break;
+                    case OutputFormat.csharp:
+                        WriteCSharpOutput(outputStream, bytecode, csharpNamespace, csharpClassName);
+                        break;
+                }
             }
         }
+        catch (MRubyCompileException ex)
+        {
+            Console.Error.WriteLine($"{inputFile}: {ex.Message}");
+            Environment.Exit(1);
+        }
     }
 
     static string GetDefaultOutputPath(string inputFile, OutputFormat format)
diff --git a/src/ChibiRuby.Compiler/CompilationResult.cs b/src/ChibiRuby.Compiler/CompilationResult.cs
index 3dbc25d..fc44290 100644
--- a/src/ChibiRuby.Compiler/CompilationResult.cs
+++ b/src/ChibiRuby.Compiler/CompilationResult.cs
@@ -49,9 +49,20 @@ internal CompilationResult(
 
     public unsafe ReadOnlySpan<byte> AsBytecode()
     {
+        if (HasError || bytecodeDataPtr == IntPtr.Zero || bytecodeLength <= 0)
+        {
+            throw new MRubyCompileException(FormatDiagnostics());
+        }
         return new ReadOnlySpan<byte>((byte*)bytecodeDataPtr, bytecodeLength);
     }
 
+    string FormatDiagnostics()
+    {
+        return Diagnostics.Count > 0
+            ? string.Join(Environment.NewLine, Diagnostics)
+            : "Ruby compilation failed (no diagnostics available).";
+    }
+
     public ReadOnlySpan<byte> AsSpan() => AsBytecode();
 
     public Irep ToIrep()
diff --git a/tests/ChibiRuby.Tests/CompilerTest.cs b/tests/ChibiRuby.Tests/CompilerTest.cs
index 325d3a3..8f60c7c 100644
--- a/tests/ChibiRuby.Tests/CompilerTest.cs
+++ b/tests/ChibiRuby.Tests/CompilerTest.cs
@@ -51,6 +51,33 @@ public void BomValidation()
         Assert.Throws<MRubyCompileException>(() => compiler.LoadSourceCode(utf32WithBom));
     }
 
+    [Test]
+    public void SyntaxError_ThrowsCompileExceptionWithDiagnostics()
+    {
+        // A bare endless range in a `when` clause is a syntax error (in CRuby too).
+        // The compiler must surface the diagnostic, not hand back empty bytecode that
+        // later blows up in the RiteParser with an opaque "Binary size is too short".
+        const string source = """
+                              case x
+                              when 10..
+                                puts "hi"
+                              end
+                              """;
+
+        var ex = Assert.Throws<MRubyCompileException>(() => compiler.LoadSourceCode(source));
+        Assert.That(ex!.Message, Does.Contain("when"));
+        Assert.That(ex.Message, Does.Not.Contain("Binary size is too short"));
+    }
+
+    [Test]
+    public void SyntaxError_CompilationResultReportsError()
+    {
+        using var compilation = compiler.Compile("when 10..\n  puts 1\n"u8);
+        Assert.That(compilation.HasError, Is.True);
+        Assert.That(compilation.Diagnostics, Is.Not.Empty);
+        Assert.Throws<MRubyCompileException>(() => _ = compilation.AsBytecode().Length);
+    }
+
     static byte[] Encode(string sourceCode, Encoding encoding)
     {
         using var ms = new MemoryStream();