diff --git a/compiler/test/stdlib/number.test.gr b/compiler/test/stdlib/number.test.gr
index 2b67caccf..b695c6ba0 100644
--- a/compiler/test/stdlib/number.test.gr
+++ b/compiler/test/stdlib/number.test.gr
@@ -987,7 +987,7 @@ assert Number.isClose( // Note: We lose a lot of precision here do to ieee754 re
 ) // Max F64
 assert Number.isClose(
   Number.sin(-1.7976931348623157e+308),
-  0.00496,
+  -0.00496,
   absoluteTolerance=1e7
 ) // Max F64
 assert Number.isNaN(Number.sin(Infinity))
@@ -1051,7 +1051,7 @@ assert Number.isClose( // Note: We lose a lot of precision here do to ieee754 re
 ) // Max F64
 assert Number.isClose(
   Number.tan(-1.7976931348623157e+308),
-  -0.00496201587,
+  0.00496201587,
   absoluteTolerance=1e7
 ) // Max F64
 assert Number.isNaN(Number.tan(Infinity))
diff --git a/stdlib/runtime/math/rempio2.gr b/stdlib/runtime/math/rempio2.gr
index ca70fe131..3c3a4fcbb 100644
--- a/stdlib/runtime/math/rempio2.gr
+++ b/stdlib/runtime/math/rempio2.gr
@@ -170,7 +170,7 @@ provide let rempio2 = (x: WasmF64, i: WasmI64, sign: Bool) => {
   let ix = WasmI32.wrapI64(i >>> 32N) & 0x7FFFFFFFn
 
   if (ix < 0x4002D97Cn) { // |x| < 3pi/4, special case with n=+-1
-    if (sign) {
+    if (!sign) {
       let z = x - pio2_1
       let mut y0 = 0.0W
       let mut y1 = 0.0W
diff --git a/stdlib/runtime/math/trig.gr b/stdlib/runtime/math/trig.gr
index b5b502268..dd6f59d5e 100644
--- a/stdlib/runtime/math/trig.gr
+++ b/stdlib/runtime/math/trig.gr
@@ -26,6 +26,8 @@ provide let sin = (x: WasmF64) => { // see: musl/src/math/sin.c
   let i = WasmI64.reinterpretF64(x)
   // Get high word of x
   let ix = WasmI32.wrapI64(i >>> 32N)
+  use WasmI32.{ (>>>) }
+  let sign = ix >>> 31n == 1n
   let ix = ix & 0x7FFFFFFFn
 
   // |x| ~< pi/4
@@ -40,8 +42,7 @@ provide let sin = (x: WasmF64) => { // see: musl/src/math/sin.c
   if (ix >= 0x7FF00000n) return x - x
 
   // argument reduction needed
-  use WasmI32.{ (>>>) }
-  let (n, y0, y1) = rempio2(x, i, ix >>> 31n == 0n)
+  let (n, y0, y1) = rempio2(x, i, sign)
   let n = fromInt32(n)
   let y0 = fromFloat64(y0)
   let y1 = fromFloat64(y1)
@@ -63,6 +64,8 @@ provide let cos = (x: WasmF64) => { // see: musl/src/math/cos.c
 
   // Get high word of x
   let ix = WasmI32.wrapI64(i >>> 32N)
+  use WasmI32.{ (>>>) }
+  let sign = ix >>> 31n == 1n
   let ix = ix & 0x7FFFFFFFn
 
   // |x| ~< pi/4
@@ -77,8 +80,7 @@ provide let cos = (x: WasmF64) => { // see: musl/src/math/cos.c
   if (ix >= 0x7FF00000n) return x - x
 
   // argument reduction needed
-  use WasmI32.{ (>>>) }
-  let (n, y0, y1) = rempio2(x, i, ix >>> 31n == 0n)
+  let (n, y0, y1) = rempio2(x, i, sign)
   let n = fromInt32(n)
   let y0 = fromFloat64(y0)
   let y1 = fromFloat64(y1)
@@ -99,6 +101,8 @@ provide let tan = (x: WasmF64) => { // see: musl/src/math/tan.c
   let i = WasmI64.reinterpretF64(x)
   // Get high word of x
   let ix = WasmI32.wrapI64(i >>> 32N)
+  use WasmI32.{ (>>>) }
+  let sign = ix >>> 31n == 1n
   let ix = ix & 0x7FFFFFFFn
 
   // |x| ~< pi/4
@@ -112,8 +116,7 @@ provide let tan = (x: WasmF64) => { // see: musl/src/math/tan.c
   // tan(Inf or NaN) is NaN
   if (ix >= 0x7FF00000n) return x - x
 
-  use WasmI32.{ (>>>) }
-  let (n, y0, y1) = rempio2(x, i, ix >>> 31n == 0n)
+  let (n, y0, y1) = rempio2(x, i, sign)
   let n = fromInt32(n)
   let y0 = fromFloat64(y0)
   let y1 = fromFloat64(y1)