diff --git a/src/libstore/builtins.cc b/src/libstore/builtins.cc
index b51b6f85c..a01dbba4e 100644
--- a/src/libstore/builtins.cc
+++ b/src/libstore/builtins.cc
@@ -42,7 +42,8 @@ void builtinFetchurl(const BasicDerivation & drv, const std::string & netrcData)
         for (auto hashedMirror : settings.hashedMirrors.get())
             try {
                 if (!hasSuffix(hashedMirror, "/")) hashedMirror += '/';
-                data = fetch(hashedMirror + getAttr("outputHashAlgo") + "/" + getAttr("outputHash"));
+                auto ht = parseHashType(getAttr("outputHashAlgo"));
+                data = fetch(hashedMirror + printHashType(ht) + "/" + Hash(getAttr("outputHash"), ht).to_string(Base16, false));
                 break;
             } catch (Error & e) {
                 debug(e.what());
diff --git a/tests/fetchurl.sh b/tests/fetchurl.sh
index 02b83525b..7f2de9070 100644
--- a/tests/fetchurl.sh
+++ b/tests/fetchurl.sh
@@ -18,6 +18,19 @@ outPath=$(nix-build '<nix/fetchurl.nix>' --argstr url file://$(pwd)/fetchurl.sh
 
 cmp $outPath fetchurl.sh
 
+# Test the hashed mirror feature.
+clearStore
+
+hash=$(nix hash-file --type sha512 --base64 ./fetchurl.sh)
+hash32=$(nix hash-file --type sha512 --base16 ./fetchurl.sh)
+
+mirror=$TMPDIR/hashed-mirror
+rm -rf $mirror
+mkdir -p $mirror/sha512
+ln -s $(pwd)/fetchurl.sh $mirror/sha512/$hash32
+
+outPath=$(nix-build '<nix/fetchurl.nix>' --argstr url file:///no-such-dir/fetchurl.sh --argstr sha512 $hash --no-out-link --option hashed-mirrors "file://$mirror")
+
 # Test unpacking a NAR.
 rm -rf $TEST_ROOT/archive
 mkdir -p $TEST_ROOT/archive