diff --git a/src/libutil/hash.cc b/src/libutil/hash.cc
index 36de293bb..e8d290d13 100644
--- a/src/libutil/hash.cc
+++ b/src/libutil/hash.cc
@@ -132,17 +132,24 @@ std::string Hash::to_string(Base base, bool includeType) const
     return s;
 }
 
-Hash fromSRI(std::string_view original) {
+Hash Hash::fromSRI(std::string_view original) {
+    auto rest = original;
 
+    // Parse the has type before the separater, if there was one.
+    auto hashRaw = splitPrefix(rest, '-');
+    if (!hashRaw)
+        throw BadHash("hash '%s' is not SRI", original);
+    HashType parsedType = parseHashType(*hashRaw);
+
+    return Hash(rest, std::make_pair(parsedType, true));
 }
 
-Hash::Hash(std::string_view s) : Hash(s, std::nullopt) { }
+Hash::Hash(std::string_view s) : Hash(s, std::nullopt) {}
 
-static HashType newFunction(std::string_view & rest, std::optional<HashType> optType)
+static std::pair<HashType, bool> newFunction(std::string_view & original, std::optional<HashType> optType)
 {
     auto rest = original;
 
-    size_t pos = 0;
     bool isSRI = false;
 
     // Parse the has type before the separater, if there was one.
@@ -166,16 +173,23 @@ static HashType newFunction(std::string_view & rest, std::optional<HashType> opt
     } else {
         if (optParsedType && optType && *optParsedType != *optType)
             throw BadHash("hash '%s' should have type '%s'", original, printHashType(*optType));
-        return optParsedType ? *optParsedType : *optType;
+        return {
+            optParsedType ? *optParsedType : *optType,
+            isSRI,
+        };
     }
 }
 
 // mutates the string_view
 Hash::Hash(std::string_view original, std::optional<HashType> optType)
-    : Hash(original, newFunction(original, optType))
+    : Hash(original, newFunction(original, optType)) {}
 
-Hash::Hash(std::string_view original, HashType type) : Hash(type) {
-    if (!isSRI && rest.size() == base16Len()) {
+Hash::Hash(std::string_view original, std::pair<HashType, bool> typeAndSRI)
+    : Hash(typeAndSRI.first)
+{
+    auto [type, isSRI] = std::move(typeAndSRI);
+
+    if (!isSRI && original.size() == base16Len()) {
 
         auto parseHexDigit = [&](char c) {
             if (c >= '0' && c <= '9') return c - '0';
@@ -186,15 +200,15 @@ Hash::Hash(std::string_view original, HashType type) : Hash(type) {
 
         for (unsigned int i = 0; i < hashSize; i++) {
             hash[i] =
-                parseHexDigit(rest[pos + i * 2]) << 4
-                | parseHexDigit(rest[pos + i * 2 + 1]);
+                parseHexDigit(original[i * 2]) << 4
+                | parseHexDigit(original[i * 2 + 1]);
         }
     }
 
-    else if (!isSRI && rest.size() == base32Len()) {
+    else if (!isSRI && original.size() == base32Len()) {
 
-        for (unsigned int n = 0; n < rest.size(); ++n) {
-            char c = rest[rest.size() - n - 1];
+        for (unsigned int n = 0; n < original.size(); ++n) {
+            char c = original[original.size() - n - 1];
             unsigned char digit;
             for (digit = 0; digit < base32Chars.size(); ++digit) /* !!! slow */
                 if (base32Chars[digit] == c) break;
@@ -214,8 +228,8 @@ Hash::Hash(std::string_view original, HashType type) : Hash(type) {
         }
     }
 
-    else if (isSRI || rest.size() == base64Len()) {
-        auto d = base64Decode(rest);
+    else if (isSRI || original.size() == base64Len()) {
+        auto d = base64Decode(original);
         if (d.size() != hashSize)
             throw BadHash("invalid %s hash '%s'", isSRI ? "SRI" : "base-64", original);
         assert(hashSize);
@@ -223,7 +237,7 @@ Hash::Hash(std::string_view original, HashType type) : Hash(type) {
     }
 
     else
-        throw BadHash("hash '%s' has wrong length for hash type '%s'", rest, printHashType(this->type));
+        throw BadHash("hash '%s' has wrong length for hash type '%s'", original, printHashType(this->type));
 }
 
 Hash newHashAllowEmpty(std::string hashStr, std::optional<HashType> ht)
diff --git a/src/libutil/hash.hh b/src/libutil/hash.hh
index 42bd585a2..570e50dd4 100644
--- a/src/libutil/hash.hh
+++ b/src/libutil/hash.hh
@@ -43,9 +43,11 @@ struct Hash
     // hash type must be part of string
     Hash(std::string_view s);
 
+    Hash fromSRI(std::string_view original);
+
 private:
     // type must be provided, s must not include <type> prefix
-    Hash(std::string_view s, HashType type);
+    Hash(std::string_view s, std::pair<HashType, bool> typeAndSRI);
 
     void init();
 
diff --git a/src/libutil/util.cc b/src/libutil/util.cc
index 1268b146a..ed43c403f 100644
--- a/src/libutil/util.cc
+++ b/src/libutil/util.cc
@@ -1433,7 +1433,7 @@ string base64Decode(std::string_view s)
 
         char digit = decode[(unsigned char) c];
         if (digit == -1)
-            throw Error("invalid character in Base64 string");
+            throw Error("invalid character in Base64 string: '%c'", c);
 
         bits += 6;
         d = d << 6 | digit;