diff --git a/src/HeaderPropagationMessageHandler.cs b/src/HeaderPropagationMessageHandler.cs
index f863998..3fa50fc 100644
--- a/src/HeaderPropagationMessageHandler.cs
+++ b/src/HeaderPropagationMessageHandler.cs
@@ -53,11 +53,31 @@ protected override Task<HttpResponseMessage> SendAsync(HttpRequestMessage reques
             {
                 var outputName = string.IsNullOrEmpty(entry?.OutboundHeaderName) ? headerName : entry.OutboundHeaderName;
 
-                if (!request.Headers.Contains(outputName) &&
-                    _values.Headers.TryGetValue(headerName, out var values) &&
-                    !StringValues.IsNullOrEmpty(values))
+                var hasContent = request.Content != null;
+
+                if (!request.Headers.TryGetValues(outputName, out var _) &&
+                    !(hasContent && request.Content.Headers.TryGetValues(outputName, out var _)))
                 {
-                    request.Headers.TryAddWithoutValidation(outputName, (string[])values);
+                    if (_values.Headers.TryGetValue(headerName, out var stringValues) &&
+                        !StringValues.IsNullOrEmpty(stringValues))
+                    {
+                        if (stringValues.Count == 1)
+                        {
+                            var value = (string)stringValues;
+                            if (!request.Headers.TryAddWithoutValidation(outputName, value) && hasContent)
+                            {
+                                request.Content.Headers.TryAddWithoutValidation(outputName, value);
+                            }
+                        }
+                        else
+                        {
+                            var values = (string[])stringValues;
+                            if (!request.Headers.TryAddWithoutValidation(outputName, values) && hasContent)
+                            {
+                                request.Content.Headers.TryAddWithoutValidation(outputName, values);
+                            }
+                        }
+                    }
                 }
             }
 
diff --git a/test/HeaderPropagationMessageHandlerTest.cs b/test/HeaderPropagationMessageHandlerTest.cs
index ebdf82f..9813cf8 100644
--- a/test/HeaderPropagationMessageHandlerTest.cs
+++ b/test/HeaderPropagationMessageHandlerTest.cs
@@ -52,6 +52,63 @@ public async Task HeaderInState_AddCorrectValue()
             Assert.Equal(new[] { "test" }, Handler.Headers.GetValues("out"));
         }
 
+        [Fact]
+        public async Task HeaderInState_WithMultipleValues_AddAllValues()
+        {
+            // Arrange
+            Configuration.Headers.Add("in", new HeaderPropagationEntry { OutboundHeaderName = "out" });
+            State.Headers.Add("in", new[] { "one", "two" });
+
+            // Act
+            await Client.SendAsync(new HttpRequestMessage());
+
+            // Assert
+            Assert.True(Handler.Headers.Contains("out"));
+            Assert.Equal(new[] { "one", "two" }, Handler.Headers.GetValues("out"));
+        }
+
+        [Fact]
+        public async Task HeaderInState_RequestWithContent_ContentHeaderPresent_DoesNotAddIt()
+        {
+            Configuration.Headers.Add("in", new HeaderPropagationEntry() { OutboundHeaderName = "Content-Type" });
+            State.Headers.Add("in", "test");
+
+            // Act
+            await Client.SendAsync(new HttpRequestMessage() { Content = new StringContent("test") });
+
+            // Assert
+            Assert.True(Handler.Content.Headers.Contains("Content-Type"));
+            Assert.Equal(new[] { "text/plain; charset=utf-8" }, Handler.Content.Headers.GetValues("Content-Type"));
+        }
+
+        [Fact]
+        public async Task HeaderInState_RequestWithContent_ContentHeaderNotPresent_AddValue()
+        {
+            Configuration.Headers.Add("in", new HeaderPropagationEntry() { OutboundHeaderName = "Content-Language" });
+            State.Headers.Add("in", "test");
+
+            // Act
+            await Client.SendAsync(new HttpRequestMessage() { Content = new StringContent("test") });
+
+            // Assert
+            Assert.True(Handler.Content.Headers.Contains("Content-Language"));
+            Assert.Equal(new[] { "test" }, Handler.Content.Headers.GetValues("Content-Language"));
+        }
+
+        [Fact]
+        public async Task HeaderInState_WithMultipleValues_RequestWithContent_ContentHeaderNotPresent_AddAllValues()
+        {
+            Configuration.Headers.Add("in", new HeaderPropagationEntry() { OutboundHeaderName = "Content-Language" });
+            State.Headers.Add("in", new[] { "one", "two" });
+
+            // Act
+            await Client.SendAsync(new HttpRequestMessage() { Content = new StringContent("test") });
+
+            // Assert
+            Assert.True(Handler.Content.Headers.Contains("Content-Language"));
+            Assert.Equal(new[] { "one", "two" }, Handler.Content.Headers.GetValues("Content-Language"));
+        }
+
         [Fact]
         public async Task HeaderInState_NoOutputName_UseInputName()
         {
@@ -168,11 +225,13 @@ public async Task NullEntryInConfiguration_AddCorrectValue()
         private class SimpleHandler : DelegatingHandler
         {
             public HttpHeaders Headers { get; private set; }
+            public HttpContent Content { get; private set; }
 
             protected override Task<HttpResponseMessage> SendAsync(HttpRequestMessage request,
                 CancellationToken cancellationToken)
             {
                 Headers = request.Headers;
+                Content = request.Content;
                 return Task.FromResult(new HttpResponseMessage());
             }
         }