diff --git a/src/ripple_data/protocol/STAmount.cpp b/src/ripple_data/protocol/STAmount.cpp
index c6dc58486..41610b126 100644
--- a/src/ripple_data/protocol/STAmount.cpp
+++ b/src/ripple_data/protocol/STAmount.cpp
@@ -223,6 +223,14 @@ std::string STAmount::createHumanCurrency (const uint160& uCurrency)
 {
     static uint160 const sIsoBits ("FFFFFFFFFFFFFFFFFFFFFFFF000000FFFFFFFFFF");
 
+    // Characters we are willing to include the ASCII representation
+    // of a three-letter currency code
+    static std::string legalASCIICurrencyCharacters =
+        "abcdefghijklmnopqrstuvwxyz"
+        "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
+        "0123456789"
+        "<>(){}[]|?!@#$%^&*";
+
     if (uCurrency.isZero ())
     {
         return SYSTEM_CURRENCY_CODE;
@@ -244,7 +252,8 @@ std::string STAmount::createHumanCurrency (const uint160& uCurrency)
 
         // Specifying the system currency code using ISO-style representation
         // is not allowed.
-        if (iso != SYSTEM_CURRENCY_CODE)
+        if ((iso != SYSTEM_CURRENCY_CODE) &&
+            (iso.find_first_not_of (legalASCIICurrencyCharacters) == std::string::npos))
             return iso;
     }