diff -up src/sage/modular/arithgroup/farey.cpp.orig src/sage/modular/arithgroup/farey.cpp
--- src/sage/modular/arithgroup/farey.cpp.orig	2017-11-08 06:03:07.383885084 -0500
+++ src/sage/modular/arithgroup/farey.cpp	2017-11-08 06:03:18.271885501 -0500
@@ -136,6 +136,7 @@ operator*(const SL2Z& M, const vector<mp
   return result;
 }
 
+#if 0
 inline 
 mpz_class 
 floor(const mpq_class r) {
@@ -146,6 +147,7 @@ floor(const mpq_class r) {
     return result - 1;
   }
 }
+#endif
 
 inline
 mpz_class lcm(const mpz_class& a, const mpz_class& b) {