diff --git a/libfixmath/fix16.hpp b/libfixmath/fix16.hpp
index dbd942b..4fcfaf3 100644
--- a/libfixmath/fix16.hpp
+++ b/libfixmath/fix16.hpp
@@ -141,14 +141,14 @@ class Fix16 {
 		const int operator> (const float other)   const { return (value >  fix16_from_float(other)); }
 		const int operator> (const int16_t other) const { return (value >  fix16_from_int(other));   }
 
-		Fix16  sin() { return Fix16(fix16_sin(value));  }
-		Fix16  cos() { return Fix16(fix16_cos(value));  }
-		Fix16  tan() { return Fix16(fix16_tan(value));  }
-		Fix16 asin() { return Fix16(fix16_asin(value)); }
-		Fix16 acos() { return Fix16(fix16_acos(value)); }
-		Fix16 atan() { return Fix16(fix16_atan(value)); }
-		Fix16 atan2(const Fix16 &inY) { return Fix16(fix16_atan2(value, inY.value)); }
-		Fix16 sqrt() { return Fix16(fix16_sqrt(value)); }
+		Fix16  sin() const { return Fix16(fix16_sin(value));  }
+		Fix16  cos() const { return Fix16(fix16_cos(value));  }
+		Fix16  tan() const { return Fix16(fix16_tan(value));  }
+		Fix16 asin() const { return Fix16(fix16_asin(value)); }
+		Fix16 acos() const { return Fix16(fix16_acos(value)); }
+		Fix16 atan() const { return Fix16(fix16_atan(value)); }
+		Fix16 atan2(const Fix16 &inY) const { return Fix16(fix16_atan2(value, inY.value)); }
+		Fix16 sqrt() const { return Fix16(fix16_sqrt(value)); }
 };
 
 #endif