diff --git a/src/Logic/BluRaySup/Core.cs b/src/Logic/BluRaySup/Core.cs
index 3877b3ab8..eb70ee0b8 100644
--- a/src/Logic/BluRaySup/Core.cs
+++ b/src/Logic/BluRaySup/Core.cs
@@ -33,19 +33,19 @@ namespace Nikse.SubtitleEdit.Logic.BluRaySup
         private const int MergePtSdiff = 18000;
 
         /** Frames per seconds for 24p (23.976) */
-        public static double Fps24P = 24000.0 / 1001;
+        public const double Fps24P = 24000.0 / 1001;
         /** Frames per seconds for wrong 24P (23.975) */
-        public static double Fps23975 = 23.975;
+        public const double Fps23975 = 23.975;
         /** Frames per seconds for 24Hz (24.0) */
-        public static double Fps24Hz = 24.0;
+        public const double Fps24Hz = 24.0;
         /** Frames per seconds for PAL progressive (25.0) */
-        public static double FpsPal = 25.0;
+        public const double FpsPal = 25.0;
         /** Frames per seconds for NTSC progressive (29.97) */
-        public static double FpsNtsc = 30000.0 / 1001;
+        public const double FpsNtsc = 30000.0 / 1001;
         /** Frames per seconds for PAL interlaced (50.0) */
-        public static double FpsPalI = 50.0;
+        public const double FpsPalI = 50.0;
         /** Frames per seconds for NTSC interlaced (59.94) */
-        public static double FpsNtscI = 60000.0 / 1001;
+        public const double FpsNtscI = 60000.0 / 1001;
 
         /**
          * Get maximum time difference for merging captions.
diff --git a/src/Logic/VideoFormats/AviRiffData.cs b/src/Logic/VideoFormats/AviRiffData.cs
index cddaf4072..bdfde9a03 100644
--- a/src/Logic/VideoFormats/AviRiffData.cs
+++ b/src/Logic/VideoFormats/AviRiffData.cs
@@ -145,7 +145,7 @@ namespace Nikse.SubtitleEdit.Logic
         //public static readonly int ckidAVIOldIndex = RiffParser.ToFourCC("idx1");
         public static readonly int ckidINFOList = RiffParser.ToFourCC("INFO");
         public static readonly int ckidAVIISFT = RiffParser.ToFourCC("ISFT");
-        public static readonly int ckidMP3 = 0x0055;
+        public const int ckidMP3 = 0x0055;
         public static readonly int ckidWaveFMT = RiffParser.ToFourCC("fmt ");
 
         #endregion
diff --git a/src/Logic/VobSub/SpHeader.cs b/src/Logic/VobSub/SpHeader.cs
index 5a6e3d12b..6b4f8645b 100644
--- a/src/Logic/VobSub/SpHeader.cs
+++ b/src/Logic/VobSub/SpHeader.cs
@@ -4,7 +4,7 @@ namespace Nikse.SubtitleEdit.Logic.VobSub
 {
     public class SpHeader
     {
-        public static int SpHeaderLength = 14;
+        public const int SpHeaderLength = 14;
 
         public string Identifier { get; private set; }
         public TimeSpan StartTime { get; private set; }