diff --git a/libm/include/math.h b/libm/include/math.h
index 6c0d4eb..3b5660f 100644
--- a/libm/include/math.h
+++ b/libm/include/math.h
@@ -484,6 +484,7 @@
 #ifdef _GNU_SOURCE
 void  sincos(double x, double *sin, double *cos);
 void  sincosf(float x, float *sin, float *cos);
+void  sincosl(long double x, long double *sin, long double *cos);
 #endif
 
 /* #endif */ /* __ISO_C_VISIBLE >= 1999 */