diff --git a/src/WireMock.Net.Abstractions/Models/IdOrTexts.cs b/src/WireMock.Net.Abstractions/Models/IdOrTexts.cs
index 7a7a03e0..6ee3c085 100644
--- a/src/WireMock.Net.Abstractions/Models/IdOrTexts.cs
+++ b/src/WireMock.Net.Abstractions/Models/IdOrTexts.cs
@@ -16,7 +16,7 @@ public readonly struct IdOrTexts
     public string? Id { get; }
 
     /// <summary>
-    /// The Text.
+    /// The Texts.
     /// </summary>
     public IReadOnlyList<string> Texts { get; }
 
@@ -41,7 +41,7 @@ public IdOrTexts(string? id, IReadOnlyList<string> texts)
     }
 
     /// <summary>
-    /// When Id is defined, return process the Id, else process the Texts.
+    /// When Id is defined, process the Id, else process the Texts.
     /// </summary>
     /// <param name="id">Callback to process the id.</param>
     /// <param name="texts">Callback to process the texts.</param>
diff --git a/src/WireMock.Net/Util/WireMockProtoFileResolver.cs b/src/WireMock.Net/Util/WireMockProtoFileResolver.cs
index 86250a1d..cbae432c 100644
--- a/src/WireMock.Net/Util/WireMockProtoFileResolver.cs
+++ b/src/WireMock.Net/Util/WireMockProtoFileResolver.cs
@@ -2,6 +2,7 @@
 
 #if PROTOBUF
 using System.Collections.Generic;
+using System.Diagnostics.CodeAnalysis;
 using System.IO;
 using System.Linq;
 using ProtoBufJsonConverter;
@@ -9,21 +10,29 @@
 
 namespace WireMock.Util;
 
+/// <summary>
+/// This resolver is used to resolve the extra ProtoDefinition files.
+/// It assumes that:
+/// - the first ProtoDefinition file is the main ProtoDefinition file.
+/// - the first commented line of each extra ProtoDefinition file is the filename which is used in the import of the other ProtoDefinition file(s).
+/// </summary>
 internal class WireMockProtoFileResolver : IProtoFileResolver
 {
     private readonly Dictionary<string, string> _files = new();
 
     public WireMockProtoFileResolver(IReadOnlyCollection<string> protoDefinitions)
     {
-        if (Guard.NotNullOrEmpty(protoDefinitions).Count() > 1)
+        if (Guard.NotNullOrEmpty(protoDefinitions).Count() <= 1)
         {
-            foreach (var extraProtoDefinition in protoDefinitions.Skip(1))
+            return;
+        }
+
+        foreach (var extraProtoDefinition in protoDefinitions.Skip(1))
+        {
+            var firstNonEmptyLine = extraProtoDefinition.Split(['\r', '\n']).FirstOrDefault(l => !string.IsNullOrEmpty(l));
+            if (firstNonEmptyLine != null && TryGetValidFileName(firstNonEmptyLine.TrimStart(['/', ' ']), out var validFileName))
             {
-                var firstNonEmptyLine = extraProtoDefinition.Split(['\r', '\n']).FirstOrDefault(l => !string.IsNullOrEmpty(l));
-                if (firstNonEmptyLine != null)
-                {
-                    _files.Add(firstNonEmptyLine.TrimStart(['\r', '\n', '/', ' ']), extraProtoDefinition);
-                }
+                _files.Add(validFileName, extraProtoDefinition);
             }
         }
     }
@@ -42,5 +51,17 @@ public TextReader OpenText(string path)
 
         throw new FileNotFoundException($"The ProtoDefinition '{path}' was not found.");
     }
+
+    private static bool TryGetValidFileName(string fileName, [NotNullWhen(true)] out string? validFileName)
+    {
+        if (!fileName.Any(c => Path.GetInvalidFileNameChars().Contains(c)))
+        {
+            validFileName = fileName;
+            return true;
+        }
+
+        validFileName = null;
+        return false;
+    }
 }
 #endif
\ No newline at end of file
diff --git a/test/WireMock.Net.Tests/Grpc/ProtoBufUtilsTests.cs b/test/WireMock.Net.Tests/Grpc/ProtoBufUtilsTests.cs
new file mode 100644
index 00000000..c8ff777c
--- /dev/null
+++ b/test/WireMock.Net.Tests/Grpc/ProtoBufUtilsTests.cs
@@ -0,0 +1,41 @@
+// Copyright © WireMock.Net
+
+#if PROTOBUF
+using System;
+using System.IO;
+using System.Threading.Tasks;
+using FluentAssertions;
+using WireMock.Util;
+using Xunit;
+
+namespace WireMock.Net.Tests.Grpc;
+
+public class ProtoBufUtilsTests
+{
+    [Fact]
+    public async Task GetProtoBufMessageWithHeader_MultipleProtoFiles()
+    {
+        // Arrange
+        var greet = await ReadProtoFileAsync("greet1.proto");
+        var request = await ReadProtoFileAsync("request.proto");
+
+        // Act
+        var responseBytes = await ProtoBufUtils.GetProtoBufMessageWithHeaderAsync(
+            [greet, request],
+            "greet.HelloRequest",
+            new
+            {
+                name = "hello"
+            }
+        );
+
+        // Assert
+        Convert.ToBase64String(responseBytes).Should().Be("AAAAAAcKBWhlbGxv");
+    }
+
+    private static Task<string> ReadProtoFileAsync(string filename)
+    {
+        return File.ReadAllTextAsync(Path.Combine(Directory.GetCurrentDirectory(), "Grpc", filename));
+    }
+}
+#endif
\ No newline at end of file
diff --git a/test/WireMock.Net.Tests/Grpc/greet1.proto b/test/WireMock.Net.Tests/Grpc/greet1.proto
new file mode 100644
index 00000000..5a263360
--- /dev/null
+++ b/test/WireMock.Net.Tests/Grpc/greet1.proto
@@ -0,0 +1,13 @@
+syntax = "proto3";
+
+import "request.proto";
+
+package greet;
+
+service Greeter {
+  rpc SayHello (HelloRequest) returns (HelloReply);
+}
+
+message HelloReply {
+  string message = 1;
+}
\ No newline at end of file
diff --git a/test/WireMock.Net.Tests/Grpc/request.proto b/test/WireMock.Net.Tests/Grpc/request.proto
new file mode 100644
index 00000000..8e9f4683
--- /dev/null
+++ b/test/WireMock.Net.Tests/Grpc/request.proto
@@ -0,0 +1,8 @@
+// request.proto
+syntax = "proto3";
+
+package greet;
+
+message HelloRequest {
+  string name = 1;
+}
\ No newline at end of file
diff --git a/test/WireMock.Net.Tests/WireMock.Net.Tests.csproj b/test/WireMock.Net.Tests/WireMock.Net.Tests.csproj
index 038dafaf..adf1c50c 100644
--- a/test/WireMock.Net.Tests/WireMock.Net.Tests.csproj
+++ b/test/WireMock.Net.Tests/WireMock.Net.Tests.csproj
@@ -134,6 +134,14 @@
         <None Update="cert.pem">
             <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
         </None>
+        <None Update="Grpc\request.proto">
+          <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
+          <!--<GrpcServices>Client</GrpcServices>-->
+        </None>
+        <None Update="Grpc\greet1.proto">
+          <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
+          <!--<GrpcServices>Client</GrpcServices>-->
+        </None>
         <None Update="Grpc\policy.proto">
           <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
           <GrpcServices>Client</GrpcServices>