diff --git a/polymer/eduke32/build/include/hightile.h b/polymer/eduke32/build/include/hightile.h
index a82bb1d2c..b2bfd1d18 100644
--- a/polymer/eduke32/build/include/hightile.h
+++ b/polymer/eduke32/build/include/hightile.h
@@ -90,6 +90,10 @@ enum
     HICEFFECTMASK = (1|2|4|8),
 };
 
+#define GRAYSCALE_COEFF_RED 0.3
+#define GRAYSCALE_COEFF_GREEN 0.59
+#define GRAYSCALE_COEFF_BLUE 0.11
+
 #ifdef __cplusplus
 }
 #endif
diff --git a/polymer/eduke32/build/src/mdsprite.c b/polymer/eduke32/build/src/mdsprite.c
index c45df8f36..e365e5636 100644
--- a/polymer/eduke32/build/src/mdsprite.c
+++ b/polymer/eduke32/build/src/mdsprite.c
@@ -622,20 +622,19 @@ static int32_t daskinloader(int32_t filh, intptr_t *fptr, int32_t *bpl, int32_t
 
             if (effect & HICTINT_GRAYSCALE)
             {
-                // greyscale
-                tcol.b = max(tcol.b, max(tcol.g, tcol.r));
-                tcol.g = tcol.r = tcol.b;
+                tcol.g = tcol.r = tcol.b = (uint8_t)((tcol.r * GRAYSCALE_COEFF_RED) + (tcol.g * GRAYSCALE_COEFF_GREEN) +
+                                                     (tcol.b * GRAYSCALE_COEFF_BLUE));
             }
+
             if (effect & HICTINT_INVERT)
             {
-                // invert
                 tcol.b = 255-tcol.b;
                 tcol.g = 255-tcol.g;
                 tcol.r = 255-tcol.r;
             }
+
             if (effect & HICTINT_COLORIZE)
             {
-                // colorize
                 tcol.b = min((int32_t)(tcol.b)*b/64,255);
                 tcol.g = min((int32_t)(tcol.g)*g/64,255);
                 tcol.r = min((int32_t)(tcol.r)*r/64,255);
diff --git a/polymer/eduke32/build/src/polymost.c b/polymer/eduke32/build/src/polymost.c
index f7e2a4ad2..360e385b4 100644
--- a/polymer/eduke32/build/src/polymost.c
+++ b/polymer/eduke32/build/src/polymost.c
@@ -1203,14 +1203,12 @@ int32_t gloadtile_hi(int32_t dapic,int32_t dapalnum, int32_t facen, hicreplctyp
 
                 if (effect & HICTINT_GRAYSCALE)
                 {
-                    // greyscale
-                    tcol.b = max(tcol.b, max(tcol.g, tcol.r));
-                    tcol.g = tcol.r = tcol.b;
+                    tcol.g = tcol.r = tcol.b = (uint8_t) ((tcol.r * GRAYSCALE_COEFF_RED) + (tcol.g * GRAYSCALE_COEFF_GREEN) +
+                                                          (tcol.b * GRAYSCALE_COEFF_BLUE));
                 }
 
                 if (effect & HICTINT_INVERT)
                 {
-                    // invert
                     tcol.b = 255-tcol.b;
                     tcol.g = 255-tcol.g;
                     tcol.r = 255-tcol.r;
@@ -1218,7 +1216,6 @@ int32_t gloadtile_hi(int32_t dapic,int32_t dapalnum, int32_t facen, hicreplctyp
 
                 if (effect & HICTINT_COLORIZE)
                 {
-                    // colorize
                     tcol.b = min((int32_t)((tcol.b)*r)/64,255);
                     tcol.g = min((int32_t)((tcol.g)*g)/64,255);
                     tcol.r = min((int32_t)((tcol.r)*b)/64,255);