diff --git a/src/libexpr/primops.cc b/src/libexpr/primops.cc
index 752176178..8e79f4953 100644
--- a/src/libexpr/primops.cc
+++ b/src/libexpr/primops.cc
@@ -1127,7 +1127,7 @@ drvName, Bindings * attrs, Value & v)
     bool contentAddressed = false;
     bool isImpure = false;
     std::optional<std::string> outputHash;
-    std::string outputHashAlgo;
+    std::optional<HashAlgorithm> outputHashAlgo;
     std::optional<ContentAddressMethod> ingestionMethod;
 
     StringSet outputs;
@@ -1226,7 +1226,7 @@ drvName, Bindings * attrs, Value & v)
                     else if (i->name == state.sOutputHash)
                         outputHash = state.forceStringNoCtx(*i->value, pos, context_below);
                     else if (i->name == state.sOutputHashAlgo)
-                        outputHashAlgo = state.forceStringNoCtx(*i->value, pos, context_below);
+                        outputHashAlgo = parseHashAlgoOpt(state.forceStringNoCtx(*i->value, pos, context_below));
                     else if (i->name == state.sOutputHashMode)
                         handleHashMode(state.forceStringNoCtx(*i->value, pos, context_below));
                     else if (i->name == state.sOutputs) {
@@ -1244,7 +1244,7 @@ drvName, Bindings * attrs, Value & v)
                     if (i->name == state.sBuilder) drv.builder = std::move(s);
                     else if (i->name == state.sSystem) drv.platform = std::move(s);
                     else if (i->name == state.sOutputHash) outputHash = std::move(s);
-                    else if (i->name == state.sOutputHashAlgo) outputHashAlgo = std::move(s);
+                    else if (i->name == state.sOutputHashAlgo) outputHashAlgo = parseHashAlgoOpt(s);
                     else if (i->name == state.sOutputHashMode) handleHashMode(s);
                     else if (i->name == state.sOutputs)
                         handleOutputs(tokenizeString<Strings>(s));
@@ -1327,7 +1327,7 @@ drvName, Bindings * attrs, Value & v)
                 "multiple outputs are not supported in fixed-output derivations"
             ).atPos(v).debugThrow();
 
-        auto h = newHashAllowEmpty(*outputHash, parseHashAlgoOpt(outputHashAlgo));
+        auto h = newHashAllowEmpty(*outputHash, outputHashAlgo);
 
         auto method = ingestionMethod.value_or(FileIngestionMethod::Flat);
 
@@ -1347,7 +1347,7 @@ drvName, Bindings * attrs, Value & v)
             state.error<EvalError>("derivation cannot be both content-addressed and impure")
                 .atPos(v).debugThrow();
 
-        auto ha = parseHashAlgoOpt(outputHashAlgo).value_or(HashAlgorithm::SHA256);
+        auto ha = outputHashAlgo.value_or(HashAlgorithm::SHA256);
         auto method = ingestionMethod.value_or(FileIngestionMethod::Recursive);
 
         for (auto & i : outputs) {