diff --git a/lib/mathlib.cpp b/lib/mathlib.cpp
index 5dfb360fe..a00cdc3b0 100644
--- a/lib/mathlib.cpp
+++ b/lib/mathlib.cpp
@@ -198,7 +198,15 @@ std::string MathLib::add(const std::string & first, const std::string & second)
     if (MathLib::isInt(first) && MathLib::isInt(second)) {
         return toString<bigint>(toLongNumber(first) + toLongNumber(second));
     }
-    return toString<double>(toDoubleNumber(first) + toDoubleNumber(second));
+
+    double d1 = toDoubleNumber(first);
+    double d2 = toDoubleNumber(second);
+    while (d1 > 100000.0 * d2 && toString<double>(d1+d2)==first)
+        d2 *= 10.0;
+    while (d2 > 100000.0 * d1 && toString<double>(d1+d2)==second)
+        d1 *= 10.0;
+
+    return toString<double>(d1 + d2);
 }
 
 std::string MathLib::subtract(const std::string &first, const std::string &second)
@@ -206,7 +214,15 @@ std::string MathLib::subtract(const std::string &first, const std::string &secon
     if (MathLib::isInt(first) && MathLib::isInt(second)) {
         return toString<bigint>(toLongNumber(first) - toLongNumber(second));
     }
-    return toString<double>(toDoubleNumber(first) - toDoubleNumber(second));
+
+    double d1 = toDoubleNumber(first);
+    double d2 = toDoubleNumber(second);
+    while (d1 > 100000.0 * d2 && toString<double>(d1-d2)==first)
+        d2 *= 10.0;
+    while (d2 > 100000.0 * d1 && toString<double>(d1-d2)==second)
+        d1 *= 10.0;
+
+    return toString<double>(d1 - d2);
 }
 
 std::string MathLib::divide(const std::string &first, const std::string &second)
diff --git a/lib/mathlib.h b/lib/mathlib.h
index 5a99bddf6..4c5a551c2 100644
--- a/lib/mathlib.h
+++ b/lib/mathlib.h
@@ -39,6 +39,7 @@ public:
     template<typename T>
     static std::string toString(const T &d) {
         std::ostringstream result;
+        result.precision(8);
         result << d;
         if (isNullValue(result.str()))
             return std::string("0");
diff --git a/test/testmathlib.cpp b/test/testmathlib.cpp
index 8519bdd56..b0ab04c57 100644
--- a/test/testmathlib.cpp
+++ b/test/testmathlib.cpp
@@ -87,6 +87,7 @@ private:
         ASSERT_EQUALS("-1" , MathLib::add("0", "-1"));
         ASSERT_EQUALS("1"  , MathLib::add("1", "0"));
         ASSERT_EQUALS("0"  , MathLib::add("0", "0."));
+        ASSERT_EQUALS("1.0000001"  , MathLib::add("1", "0.00000001"));  // #4016
 
         // subtraction
         ASSERT_EQUALS("254", MathLib::subtract("0xff", "1"));
@@ -96,6 +97,7 @@ private:
         ASSERT_EQUALS("1"  , MathLib::subtract("0", "-1"));
         ASSERT_EQUALS("1"  , MathLib::subtract("1", "0"));
         ASSERT_EQUALS("0"  , MathLib::subtract("0", "0."));
+        ASSERT_EQUALS("0.99999999"  , MathLib::subtract("1", "0.00000001")); // #4016
 
         // multiply
         ASSERT_EQUALS("-0.003"          , MathLib::multiply("-1e-3", "3"));