diff --git a/lib/mathlib.cpp b/lib/mathlib.cpp
index d6c76634b..011423c35 100644
--- a/lib/mathlib.cpp
+++ b/lib/mathlib.cpp
@@ -287,7 +287,7 @@ std::string MathLib::divide(const std::string &first, const std::string &second)
             throw InternalError(0, "Internal Error: Division by zero");
         return toString(toLongNumber(first) / b);
     } else if (second == "0.0") {
-        return "inf.0";
+        return (first[0] == '-') ? "-inf.0" : "inf.0";
     }
     return toString(toDoubleNumber(first) / toDoubleNumber(second));
 }
diff --git a/test/testmathlib.cpp b/test/testmathlib.cpp
index 1066b6deb..27882cf5c 100644
--- a/test/testmathlib.cpp
+++ b/test/testmathlib.cpp
@@ -377,7 +377,7 @@ private:
     void naninf() {
         ASSERT_EQUALS("inf.0", MathLib::divide("0.0", "0.0")); // nan
         ASSERT_EQUALS("inf.0", MathLib::divide("3.0", "0.0")); // inf
-        ASSERT_EQUALS("inf.0", MathLib::divide("-3.0", "0.0")); // -inf
+        ASSERT_EQUALS("-inf.0", MathLib::divide("-3.0", "0.0")); // -inf (#5142)
     }
 };