diff --git a/fractional/src/trigonometry.rs b/fractional/src/trigonometry.rs
index 580bcfd..f43ed38 100644
--- a/fractional/src/trigonometry.rs
+++ b/fractional/src/trigonometry.rs
@@ -45,7 +45,9 @@ pub trait Trig {
             91 ..=180 => Self::sintab()[180 - d as usize],
             181..=270 => -Self::sintab()[d as usize - 180],
             271..=359 => -Self::sintab()[360 - d as usize],
-            _         => Self::sin(d % 360),
+            _         => {
+                Self::sin(if d < 0 { d % 360 + 360 } else { d % 360 })
+            },
         }
     }
 
@@ -56,7 +58,9 @@ pub trait Trig {
             91 ..=180 => -Self::sintab()[90 - (180 - d as usize)],
             181..=270 => -Self::sintab()[90 - (d as usize - 180)],
             271..=359 => Self::sintab()[90 - (360 - d as usize)],
-            _         => Self::cos(d % 360),
+            _         => {
+                Self::cos(if d < 0 { d % 360 + 360 } else { d % 360 })
+            },
         }
     }
 
@@ -64,7 +68,9 @@ pub trait Trig {
         match d {
             0  ..=179 => Self::tantab()[d as usize],
             180..=359 => Self::tantab()[d as usize - 180],
-            _         => Self::tan(d % 360),
+            _         => {
+                Self::tan(if d < 0 { d % 360 + 360 } else { d % 360 })
+            },
         }
     }
 }