diff --git a/lib/mathlib.cpp b/lib/mathlib.cpp
index 837441ff5..aa0ee2607 100644
--- a/lib/mathlib.cpp
+++ b/lib/mathlib.cpp
@@ -368,9 +368,7 @@ bool MathLib::isHex(const std::string& s)
 
 bool MathLib::isValidSuffix(std::string::const_iterator it, std::string::const_iterator end)
 {
-    enum Status {
-        START, SUFFIX_U, SUFFIX_UL, SUFFIX_ULL, SUFFIX_L, SUFFIX_LU, SUFFIX_LL, SUFFIX_LLU
-    } state = START;
+    enum {START, SUFFIX_U, SUFFIX_UL, SUFFIX_ULL, SUFFIX_L, SUFFIX_LU, SUFFIX_LL, SUFFIX_LLU, SUFFIX_I, SUFFIX_I6, SUFFIX_I64} state = START;
     for (; it != end; ++it) {
         switch (state) {
         case START:
@@ -378,6 +376,8 @@ bool MathLib::isValidSuffix(std::string::const_iterator it, std::string::const_i
                 state = SUFFIX_U;
             else if (*it == 'l' || *it == 'L')
                 state = SUFFIX_L;
+            else if (*it == 'i')
+                state = SUFFIX_I;
             else
                 return false;
             break;
@@ -409,13 +409,31 @@ bool MathLib::isValidSuffix(std::string::const_iterator it, std::string::const_i
             else
                 return false;
             break;
+        case SUFFIX_I:
+            if (*it == '6')
+                state = SUFFIX_I6;
+            else
+                return false;
+            break;
+        case SUFFIX_I6:
+            if (*it == '4')
+                state = SUFFIX_I64;
+            else
+                return false;
+            break;
         default:
             return false;
+            break;
         }
     }
-    return (state == SUFFIX_U)  || (state == SUFFIX_L)
-           || (state == SUFFIX_UL) || (state == SUFFIX_LU)   || (state == SUFFIX_LL)
-           || (state == SUFFIX_ULL) || (state == SUFFIX_LLU);
+    return ((state == SUFFIX_U)   ||
+            (state == SUFFIX_L)   ||
+            (state == SUFFIX_UL)  ||
+            (state == SUFFIX_LU)  ||
+            (state == SUFFIX_LL)  ||
+            (state == SUFFIX_ULL) ||
+            (state == SUFFIX_LLU) ||
+            (state == SUFFIX_I64));
 }
 
 /*! \brief Does the string represent a binary number?
diff --git a/test/testmathlib.cpp b/test/testmathlib.cpp
index c353b7700..fc1360ca0 100644
--- a/test/testmathlib.cpp
+++ b/test/testmathlib.cpp
@@ -36,6 +36,7 @@ private:
         TEST_CASE(isdec);
         TEST_CASE(isoct);
         TEST_CASE(ishex);
+        TEST_CASE(isValidSuffix);
         TEST_CASE(isnegative);
         TEST_CASE(ispositive);
         TEST_CASE(isfloat);
@@ -533,6 +534,77 @@ private:
         ASSERT_EQUALS(false, MathLib::isHex(""));
     }
 
+    void isValidSuffix(void)
+    {
+        // negative testing
+        std::string value = "ux";
+        ASSERT_EQUALS(false, MathLib::isValidSuffix(value.begin(), value.end()));
+
+        value = "ulx";
+        ASSERT_EQUALS(false, MathLib::isValidSuffix(value.begin(), value.end()));
+
+        value = "lx";
+        ASSERT_EQUALS(false, MathLib::isValidSuffix(value.begin(), value.end()));
+
+        value = "lux";
+        ASSERT_EQUALS(false, MathLib::isValidSuffix(value.begin(), value.end()));
+
+        value = "lll";
+        ASSERT_EQUALS(false, MathLib::isValidSuffix(value.begin(), value.end()));
+
+        value = "garbage";
+        ASSERT_EQUALS(false, MathLib::isValidSuffix(value.begin(), value.end()));
+
+        value = "";
+        ASSERT_EQUALS(false, MathLib::isValidSuffix(value.begin(), value.end()));
+
+        value = "llu ";
+        ASSERT_EQUALS(false, MathLib::isValidSuffix(value.begin(), value.end()));
+
+        value = "i";
+        ASSERT_EQUALS(false, MathLib::isValidSuffix(value.begin(), value.end()));
+
+        value = "iX";
+        ASSERT_EQUALS(false, MathLib::isValidSuffix(value.begin(), value.end()));
+
+        value = "i6X";
+        ASSERT_EQUALS(false, MathLib::isValidSuffix(value.begin(), value.end()));
+
+        value = "i64X";
+        ASSERT_EQUALS(false, MathLib::isValidSuffix(value.begin(), value.end()));
+
+        value = "i64 ";
+        ASSERT_EQUALS(false, MathLib::isValidSuffix(value.begin(), value.end()));
+
+        value = "i66";
+        ASSERT_EQUALS(false, MathLib::isValidSuffix(value.begin(), value.end()));
+
+        // positive testing
+        value = "u";
+        ASSERT_EQUALS(true, MathLib::isValidSuffix(value.begin(), value.end()));
+
+        value = "ul";
+        ASSERT_EQUALS(true, MathLib::isValidSuffix(value.begin(), value.end()));
+
+        value = "ull";
+        ASSERT_EQUALS(true, MathLib::isValidSuffix(value.begin(), value.end()));
+
+        value = "l";
+        ASSERT_EQUALS(true, MathLib::isValidSuffix(value.begin(), value.end()));
+
+        value = "lu";
+        ASSERT_EQUALS(true, MathLib::isValidSuffix(value.begin(), value.end()));
+
+        value = "ll";
+        ASSERT_EQUALS(true, MathLib::isValidSuffix(value.begin(), value.end()));
+
+        value = "llu";
+        ASSERT_EQUALS(true, MathLib::isValidSuffix(value.begin(), value.end()));
+
+        value = "i64";
+        ASSERT_EQUALS(true, MathLib::isValidSuffix(value.begin(), value.end()));
+    }
+
     void ispositive() const
     {
         ASSERT_EQUALS(false, MathLib::isPositive("-1"));