diff --git a/ChangeLog b/ChangeLog
index aa937460d4..8c481a0b6f 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,11 @@
+2023-01-13 Frederik Seiffert <frederik@algoriddim.com>
+
+	* Source/Additions/GSInsensitiveDictionary.m:
+	* Source/NSURLRequest.m:
+	* Source/NSURLResponse.m:
+	Fix NSURLSession header fields not always being matched case
+	insensitive.
+
 2023-01-13 Frederik Seiffert <frederik@algoriddim.com>
 
 	* Source/GSEasyHandle.m:
diff --git a/Source/Additions/GSInsensitiveDictionary.m b/Source/Additions/GSInsensitiveDictionary.m
index 6400bb57b1..b383ed0009 100644
--- a/Source/Additions/GSInsensitiveDictionary.m
+++ b/Source/Additions/GSInsensitiveDictionary.m
@@ -378,6 +378,13 @@ - (id) copyWithZone: (NSZone*)zone
   return [copy initWithDictionary: self copyItems: NO];
 }
 
+- (id) mutableCopyWithZone: (NSZone*)z
+{
+  NSMutableDictionary	*copy = [_GSMutableInsensitiveDictionary allocWithZone: z];
+
+  return [copy initWithDictionary: self copyItems: NO];
+}
+
 - (id) init
 {
   return [self initWithCapacity: 0];
diff --git a/Source/Additions/GSMime.m b/Source/Additions/GSMime.m
index aa4d5e369c..7478ded754 100644
--- a/Source/Additions/GSMime.m
+++ b/Source/Additions/GSMime.m
@@ -3345,7 +3345,6 @@ - (BOOL) _scanHeaderParameters: (NSScanner*)scanner into: (GSMimeHeader*)info
 
 @end
 
-
 
 @interface	_GSMutableInsensitiveDictionary : NSMutableDictionary
 @end
diff --git a/Source/NSURLRequest.m b/Source/NSURLRequest.m
index beed313a78..b079df8f6b 100644
--- a/Source/NSURLRequest.m
+++ b/Source/NSURLRequest.m
@@ -118,7 +118,7 @@ - (id) copyWithZone: (NSZone*)z
 	  inst->shouldHandleCookies = this->shouldHandleCookies;
 	  inst->debug = this->debug;
 	  inst->ioDelegate = this->ioDelegate;
-          inst->headers = [this->headers mutableCopy];
+	  inst->headers = [this->headers mutableCopy];
 	}
     }
   return o;
diff --git a/Source/NSURLResponse.m b/Source/NSURLResponse.m
index c68fc2fa17..3e013b39d0 100644
--- a/Source/NSURLResponse.m
+++ b/Source/NSURLResponse.m
@@ -284,8 +284,15 @@ - (id) initWithURL: (NSURL*)URL
 	  textEncodingName: nil];
   if (nil != self)
     {
+      NSString *k;
+      NSEnumerator *e = [headerFields keyEnumerator];
+      while (nil != (k = [e nextObject]))
+        {
+          NSString *v = [headerFields objectForKey: k];
+          [self _setValue: v forHTTPHeaderField: k];
+        }
+
       this->statusCode = statusCode;
-      this->headers = [headerFields copy];
       [self _checkHeaders];
     }
   return self;