diff --git a/reSID/envelope.cc b/reSID/envelope.cc
index 14e93e3..915c4c4 100644
--- a/reSID/envelope.cc
+++ b/reSID/envelope.cc
@@ -98,7 +98,7 @@ void EnvelopeGenerator::reset()
 // The described method is thus sufficient for exact calculation of the rate
 // periods.
 //
-reg16 EnvelopeGenerator::rate_counter_period[] = {
+const reg16 EnvelopeGenerator::rate_counter_period[] = {
       9,  //   2ms*1.0MHz/256 =     7.81
      32,  //   8ms*1.0MHz/256 =    31.25
      63,  //  16ms*1.0MHz/256 =    62.50
@@ -155,7 +155,7 @@ reg16 EnvelopeGenerator::rate_counter_period[] = {
 // envelope counter are compared to the 4-bit sustain value.
 // This has been verified by sampling ENV3.
 //
-reg8 EnvelopeGenerator::sustain_level[] = {
+const reg8 EnvelopeGenerator::sustain_level[] = {
   0x00,
   0x11,
   0x22,
diff --git a/reSID/envelope.h b/reSID/envelope.h
index 5574953..7fd86ee 100644
--- a/reSID/envelope.h
+++ b/reSID/envelope.h
@@ -71,10 +71,10 @@ protected:
 
   // Lookup table to convert from attack, decay, or release value to rate
   // counter period.
-  static reg16 rate_counter_period[];
+  static const reg16 rate_counter_period[];
 
   // The 16 selectable sustain levels.
-  static reg8 sustain_level[];
+  static const reg8 sustain_level[];
 
 friend class SID;
 };
diff --git a/reSID/filter.cc b/reSID/filter.cc
index ecd7415..83deb4e 100644
--- a/reSID/filter.cc
+++ b/reSID/filter.cc
@@ -44,7 +44,7 @@ RESID_NAMESPACE_START
 // NB! Cutoff frequency characteristics may vary, we have modeled two
 // particular Commodore 64s.
 
-fc_point Filter::f0_points_6581[] =
+const fc_point Filter::f0_points_6581[] =
 {
   //  FC      f         FCHI FCLO
   // ----------------------------
@@ -81,7 +81,7 @@ fc_point Filter::f0_points_6581[] =
   { 2047, 18000 }    // 0xff 0x07 - repeated end point
 };
 
-fc_point Filter::f0_points_8580[] =
+const fc_point Filter::f0_points_8580[] =
 {
   //  FC      f         FCHI FCLO
   // ----------------------------
diff --git a/reSID/filter.h b/reSID/filter.h
index 1ebcc56..4afbb68 100644
--- a/reSID/filter.h
+++ b/reSID/filter.h
@@ -193,9 +193,9 @@ protected:
   sound_sample f0_6581[2048];
   sound_sample f0_8580[2048];
   sound_sample* f0;
-  static fc_point f0_points_6581[];
-  static fc_point f0_points_8580[];
-  fc_point* f0_points;
+  const static fc_point f0_points_6581[];
+  const static fc_point f0_points_8580[];
+  const fc_point* f0_points;
   int f0_count;
 
 friend class SID;