diff --git a/src/util/strencodings.h b/src/util/strencodings.h
--- a/src/util/strencodings.h
+++ b/src/util/strencodings.h
@@ -52,7 +52,7 @@
 /**
  * Return true if the string is a hex number, optionally prefixed with "0x"
  */
-bool IsHexNumber(const std::string &str);
+bool IsHexNumber(const std::string &str) noexcept;
 std::vector<uint8_t> DecodeBase64(const char *p, bool *pfInvalid = nullptr);
 std::string DecodeBase64(const std::string &str);
 std::string EncodeBase64(const uint8_t *pch, size_t len);
diff --git a/src/util/strencodings.cpp b/src/util/strencodings.cpp
--- a/src/util/strencodings.cpp
+++ b/src/util/strencodings.cpp
@@ -67,18 +67,22 @@
     return (str.size() > 0) && (str.size() % 2 == 0);
 }
 
-bool IsHexNumber(const std::string &str) {
+bool IsHexNumber(const std::string &string) noexcept {
     size_t starting_location = 0;
-    if (str.size() > 2 && *str.begin() == '0' && *(str.begin() + 1) == 'x') {
-        starting_location = 2;
-    }
-    for (auto c : str.substr(starting_location)) {
-        if (HexDigit(c) < 0) {
-            return false;
+    try {
+        if (string.substr(0, 2) == "0x") {
+            starting_location = 2;
         }
+    } catch (const std::out_of_range &oor) {
+    } // substr(0,x) should never throw out_of_range, but hey, compilers
+
+    // if string is just "" or "0x", return false
+    if (string.size() == starting_location) {
+        return false;
     }
-    // Return false for empty string or "0x".
-    return (str.size() > starting_location);
+
+    return string.find_first_not_of("0123456789abcdefABCDEF",
+                                    starting_location) == std::string::npos;
 }
 
 std::vector<uint8_t> ParseHex(const char *psz) {