diff --git a/components/fpspreadsheet/source/common/fpsreaderwriter.pas b/components/fpspreadsheet/source/common/fpsreaderwriter.pas
index e1c5f72c8..db22b8a38 100644
--- a/components/fpspreadsheet/source/common/fpsreaderwriter.pas
+++ b/components/fpspreadsheet/source/common/fpsreaderwriter.pas
@@ -364,7 +364,7 @@ end;
 class function TsCustomSpreadReader.CheckFileFormat(AStream: TStream): boolean;
 begin
   Unused(AStream);
-  Result := true;
+  Result := not HasZipHeader(AStream);
 end;
 
 {@@ ----------------------------------------------------------------------------
diff --git a/components/fpspreadsheet/source/common/fpsutils.pas b/components/fpspreadsheet/source/common/fpsutils.pas
index bb8bfcf81..89bda3db1 100644
--- a/components/fpspreadsheet/source/common/fpsutils.pas
+++ b/components/fpspreadsheet/source/common/fpsutils.pas
@@ -212,6 +212,7 @@ procedure InitHeaderFooterImageRecord(out AImage: TsHeaderFooterImage);
 //procedure CopyCellValue(AFromCell, AToCell: PCell);
 function HasFormula(ACell: PCell): Boolean;
 function Has3dFormula(ACell: PCell): Boolean;
+function HasZipHeader(AStream: TStream): Boolean;
 function SameCellBorders(AFormat1, AFormat2: PsCellFormat): Boolean;
 function SameFont(AFont1, AFont2: TsFont): Boolean; overload;
 function SameFont(AFont: TsFont; AFontName: String; AFontSize: Single;
@@ -2552,6 +2553,29 @@ begin
 end;
 
 {@@ ----------------------------------------------------------------------------
+  Returns true if the file begins with a ZIP header *PK'#03#04.
+  Needed for file format detection.
+-------------------------------------------------------------------------------}
+function HasZipHeader(AStream: TStream): Boolean;
+const
+  ZIP_HEADER: packed array[0..3] of char = ('P', 'K', #03, #04);
+var
+  P: Int64;
+  buf: packed array[0..3] of char = (#0, #0, #0, #0);
+begin
+  Result := false;
+  P := AStream.Position;
+  try
+    AStream.Position := 0;
+    if AStream.Read(buf, 4) < 4 then
+      exit;
+    Result := CompareMem(@buf[0], @ZIP_HEADER[0], 4);
+  finally
+    AStream.Position := P;
+  end;
+end;
+
+{-------------------------------------------------------------------------------
   Checks whether two format records have same border attributes
 
   @param  AFormat1  Pointer to the first one of the two format records to be compared
diff --git a/components/fpspreadsheet/source/common/fpsxmlcommon.pas b/components/fpspreadsheet/source/common/fpsxmlcommon.pas
index c970c8465..8db007e5e 100644
--- a/components/fpspreadsheet/source/common/fpsxmlcommon.pas
+++ b/components/fpspreadsheet/source/common/fpsxmlcommon.pas
@@ -57,8 +57,6 @@ function CreateTempStream(AWorkbook: TsBasicWorkbook;
   AFileNameBase: String): TStream;
 procedure DestroyTempStream(AStream: TStream);
 
-function HasZipHeader(AStream: TStream): Boolean;
-
 
 implementation
 
@@ -394,7 +392,6 @@ begin
     Result := TMemoryStream.Create;
 end;
 
-
 procedure DestroyTempStream(AStream: TStream);
 var
   fn: String;
@@ -412,26 +409,5 @@ begin
 end;
 
 
-{ Returns true if the file begins with a ZIP header *PK'. Needed for
-  file format detection. }
-function HasZipHeader(AStream: TStream): Boolean;
-const
-  ZIP_HEADER: packed array[0..1] of char = ('P', 'K');
-var
-  P: Int64;
-  buf: packed array[0..1] of char = (#0, #0);
-begin
-  Result := false;
-  P := AStream.Position;
-  try
-    AStream.Position := 0;
-    if AStream.Read(buf, 2) < 2 then
-      exit;
-    Result := (buf[0] = ZIP_HEADER[0]) and (buf[1] = ZIP_HEADER[1]);
-  finally
-    AStream.Position := P;
-  end;
-end;
-
 end.