diff --git a/lib/mathlib.cpp b/lib/mathlib.cpp
index 6490d398d..c43d239a3 100644
--- a/lib/mathlib.cpp
+++ b/lib/mathlib.cpp
@@ -31,10 +31,17 @@ MathLib::bigint MathLib::toLongNumber(const std::string &str)
 {
     // hexadecimal numbers:
     if (isHex(str)) {
-        bigint ret = 0;
-        std::istringstream istr(str);
-        istr >> std::hex >> ret;
-        return ret;
+        if (str[0] == '-') {
+            bigint ret = 0;
+            std::istringstream istr(str);
+            istr >> std::hex >> ret;
+            return ret;
+        } else {
+            unsigned long long ret = 0;
+            std::istringstream istr(str);
+            istr >> std::hex >> ret;
+            return (bigint)ret;
+        }
     }
 
     // octal numbers:
diff --git a/test/testmathlib.cpp b/test/testmathlib.cpp
index f0e2eb994..232b66a81 100644
--- a/test/testmathlib.cpp
+++ b/test/testmathlib.cpp
@@ -185,6 +185,10 @@ private:
         ASSERT_EQUALS(100   , MathLib::toLongNumber("+10.0E+1"));
         ASSERT_EQUALS(-1    , MathLib::toLongNumber("-10.0E-1"));
 
+        // from long long
+        ASSERT_EQUALS(0xFF00000000000000LL, MathLib::toLongNumber("0xFF00000000000000LL"));
+        ASSERT_EQUALS(0x0A00000000000000LL, MathLib::toLongNumber("0x0A00000000000000LL"));
+
         // -----------------
         // to double number:
         // -----------------