diff --git a/lib/mathlib.cpp b/lib/mathlib.cpp
index 6d98cbea9..dcccbe818 100644
--- a/lib/mathlib.cpp
+++ b/lib/mathlib.cpp
@@ -356,6 +356,8 @@ MathLib::bigint MathLib::characterLiteralToLongNumber(const std::string& str)
     // is implementation-defined.
     // clang and gcc seem to use the following encoding: 'AB' as (('A' << 8) | 'B')
     const std::string& normStr = normalizeCharacterLiteral(str);
+    if (normStr.empty())
+        throw InternalError(0, "Internal Error. MathLib::characterLiteralToLongNumber: Unhandled char constant '" + str + "'.");
     return encodeMultiChar(normStr);
 }
 
diff --git a/test/testmathlib.cpp b/test/testmathlib.cpp
index 8cc7258d1..ca569e103 100644
--- a/test/testmathlib.cpp
+++ b/test/testmathlib.cpp
@@ -301,6 +301,7 @@ private:
             ASSERT_EQUALS(0, MathLib::characterLiteralToLongNumber(std::string("")));
             ASSERT_EQUALS(32, MathLib::characterLiteralToLongNumber(std::string(" ")));
             ASSERT_EQUALS(538976288, MathLib::characterLiteralToLongNumber(std::string("          ")));
+            ASSERT_THROW(MathLib::characterLiteralToLongNumber(std::string("\\u")), InternalError);
         }
 
         ASSERT_EQUALS(-8552249625308161526, MathLib::toLongNumber("0x89504e470d0a1a0a"));