diff --git a/src/libm/math.h b/src/libm/math.h
index 15008e31b..723d595df 100644
--- a/src/libm/math.h
+++ b/src/libm/math.h
@@ -36,6 +36,7 @@ extern double __ieee754_sqrt(double x);
 extern double copysign(double x, double y);
 extern double cos(double x);
 extern double fabs(double x);
+extern double floor(double x);
 extern double scalbn(double x, int n);
 extern double sin(double x);