4 files changed, 8 insertions, 2 deletions
diff --git a/src/buildtool/build_engine/target_map/utils.cpp b/src/buildtool/build_engine/target_map/utils.cpp
index 0ecda4ce..5bdeffe5 100644
--- a/src/buildtool/build_engine/target_map/utils.cpp
+++ b/src/buildtool/build_engine/target_map/utils.cpp
@@ -262,6 +262,7 @@ auto BuildMaps::Target::Utils::createAction(
     HashFunction hash_function{HashFunction::Type::PlainSHA256};
     auto hasher = hash_function.MakeHasher();
 
+    hasher.Update("ACTION:");
     hasher.Update(hash_vector(hash_function, output_files));
     hasher.Update(hash_vector(hash_function, output_dirs));
     hasher.Update(hash_vector(hash_function, command));
diff --git a/src/buildtool/common/TARGETS b/src/buildtool/common/TARGETS
index 19bad797..469f074f 100644
--- a/src/buildtool/common/TARGETS
+++ b/src/buildtool/common/TARGETS
@@ -153,6 +153,7 @@
     [ "action_description"
     , "artifact_description"
     , "common"
+    , ["@", "fmt", "", "fmt"]
     , ["@", "json", "", "json"]
     , ["src/buildtool/crypto", "hash_function"]
     ]
diff --git a/src/buildtool/common/tree.hpp b/src/buildtool/common/tree.hpp
index c861b264..bf81d848 100644
--- a/src/buildtool/common/tree.hpp
+++ b/src/buildtool/common/tree.hpp
@@ -22,6 +22,7 @@
 #include <unordered_map>
 #include <utility>
 
+#include "fmt/core.h"
 #include "nlohmann/json.hpp"
 #include "src/buildtool/common/action.hpp"
 #include "src/buildtool/common/action_description.hpp"
@@ -91,7 +92,9 @@ class Tree {
         // The type of HashFunction is irrelevant here. It is used for
         // identification of trees. SHA256 is used.
         HashFunction const hash_function{HashFunction::Type::PlainSHA256};
-        return hash_function.PlainHashData(ComputeDescription(inputs).dump())
+        return hash_function
+            .PlainHashData(
+                fmt::format("TREE:{}", ComputeDescription(inputs).dump()))
             .HexString();
     }
 };
diff --git a/src/buildtool/common/tree_overlay.hpp b/src/buildtool/common/tree_overlay.hpp
index 1b7faaed..69b992a2 100644
--- a/src/buildtool/common/tree_overlay.hpp
+++ b/src/buildtool/common/tree_overlay.hpp
@@ -103,7 +103,8 @@ class TreeOverlay {
         // identification of trees. SHA256 is used.
         HashFunction const hash_function{HashFunction::Type::PlainSHA256};
         return hash_function
-            .PlainHashData(ComputeDescription(trees, disjoint).dump())
+            .PlainHashData(fmt::format(
+                "TREE_OVERLAY:{}", ComputeDescription(trees, disjoint).dump()))
             .HexString();
     }