3 files changed, 14 insertions, 3 deletions
diff --git a/src/libstore/daemon.cc b/src/libstore/daemon.cc
index 242b4ddc6..420fc8bfe 100644
--- a/src/libstore/daemon.cc
+++ b/src/libstore/daemon.cc
@@ -527,7 +527,7 @@ static void performOp(TunnelLogger * logger, ref<Store> store,
         auto drvs = WorkerProto::Serialise<DerivedPaths>::read(*store, rconn);
         BuildMode mode = bmNormal;
         if (GET_PROTOCOL_MINOR(clientVersion) >= 15) {
-            mode = (BuildMode) readInt(from);
+            mode = buildModeFromInteger(readInt(from));
 
             /* Repairing is not atomic, so disallowed for "untrusted"
                clients.
@@ -551,7 +551,7 @@ static void performOp(TunnelLogger * logger, ref<Store> store,
     case WorkerProto::Op::BuildPathsWithResults: {
         auto drvs = WorkerProto::Serialise<DerivedPaths>::read(*store, rconn);
         BuildMode mode = bmNormal;
-        mode = (BuildMode) readInt(from);
+        mode = buildModeFromInteger(readInt(from));
 
         /* Repairing is not atomic, so disallowed for "untrusted"
            clients.
@@ -582,7 +582,7 @@ static void performOp(TunnelLogger * logger, ref<Store> store,
          * correctly.
          */
         readDerivation(from, *store, drv, Derivation::nameFromPath(drvPath));
-        BuildMode buildMode = (BuildMode) readInt(from);
+        BuildMode buildMode = buildModeFromInteger(readInt(from));
         logger->startWork();
 
         auto drvType = drv.type();
diff --git a/src/libstore/store-api.cc b/src/libstore/store-api.cc
index 509b0fa68..ed3566f5e 100644
--- a/src/libstore/store-api.cc
+++ b/src/libstore/store-api.cc
@@ -22,6 +22,14 @@ using json = nlohmann::json;
 
 namespace nix {
 
+BuildMode buildModeFromInteger(int raw) {
+    switch (raw) {
+    case bmNormal: return bmNormal;
+    case bmRepair: return bmRepair;
+    case bmCheck: return bmCheck;
+    default: throw Error("Invalid BuildMode");
+    }
+}
 
 bool Store::isInStore(PathView path) const
 {
diff --git a/src/libstore/store-api.hh b/src/libstore/store-api.hh
index 47e644fed..745fce594 100644
--- a/src/libstore/store-api.hh
+++ b/src/libstore/store-api.hh
@@ -90,6 +90,9 @@ const uint32_t exportMagic = 0x4558494e;
 
 
 enum BuildMode { bmNormal, bmRepair, bmCheck };
+/** Checks that a build mode is a valid one, then returns it */
+BuildMode buildModeFromInteger(int);
+
 enum TrustedFlag : bool { NotTrusted = false, Trusted = true };
 
 struct BuildResult;