diff --git a/lib/mathlib.cpp b/lib/mathlib.cpp
index 403662f4df2..c7c055899fd 100644
--- a/lib/mathlib.cpp
+++ b/lib/mathlib.cpp
@@ -266,7 +266,7 @@ MathLib::value MathLib::value::shiftLeft(const MathLib::value &v) const
     if (!isInt() || !v.isInt())
         throw InternalError(nullptr, "Shift operand is not integer");
     MathLib::value ret(*this);
-    if (v.mIntValue >= MathLib::bigint_bits) {
+    if (v.mIntValue < 0 || v.mIntValue >= MathLib::bigint_bits || ret.mIntValue < 0) {
         return ret;
     }
     ret.mIntValue <<= v.mIntValue;
@@ -278,7 +278,7 @@ MathLib::value MathLib::value::shiftRight(const MathLib::value &v) const
     if (!isInt() || !v.isInt())
         throw InternalError(nullptr, "Shift operand is not integer");
     MathLib::value ret(*this);
-    if (v.mIntValue >= MathLib::bigint_bits) {
+    if (v.mIntValue < 0 || v.mIntValue >= MathLib::bigint_bits) {
         return ret;
     }
     ret.mIntValue >>= v.mIntValue;
diff --git a/test/testmathlib.cpp b/test/testmathlib.cpp
index 8cbe5b50019..4133d710e4f 100644
--- a/test/testmathlib.cpp
+++ b/test/testmathlib.cpp
@@ -64,6 +64,7 @@ class TestMathLib : public TestFixture {
         TEST_CASE(tan);
         TEST_CASE(abs);
         TEST_CASE(toString);
+        TEST_CASE(valueShift);
     }
 
     void isGreater() const {
@@ -1511,6 +1512,20 @@ class TestMathLib : public TestFixture {
         ASSERT_EQUALS("2.22507385851e-308", MathLib::toString(std::numeric_limits<double>::min()));
         ASSERT_EQUALS("1.79769313486e+308", MathLib::toString(std::numeric_limits<double>::max()));
     }
+
+    void valueShift() const {
+        // ordinary shifts
+        ASSERT_EQUALS("16", (MathLib::value("1") << MathLib::value("4")).str());
+        ASSERT_EQUALS("64", (MathLib::value("256") >> MathLib::value("2")).str());
+
+        // a large hex literal is not negative as a string but parses to a negative
+        // bigint; shifting it must not be performed (left shift of a negative value
+        // and shifting by a negative count are both undefined). the operand is
+        // returned unchanged, as already done for counts >= bigint_bits.
+        ASSERT_EQUALS("9223372036854775808U", (MathLib::value("0x8000000000000000") << MathLib::value("1")).str());
+        ASSERT_EQUALS("1", (MathLib::value("1") << MathLib::value("0x8000000000000000")).str());
+        ASSERT_EQUALS("1", (MathLib::value("1") >> MathLib::value("0x8000000000000000")).str());
+    }
 };
 
 REGISTER_TEST(TestMathLib)