diff --git a/crates/project-model/src/project_json.rs b/crates/project-model/src/project_json.rs
index 6938010cbd..cbbb95cc46 100644
--- a/crates/project-model/src/project_json.rs
+++ b/crates/project-model/src/project_json.rs
@@ -368,6 +368,9 @@ pub enum RunnableKind {
     /// Template for checking a target, emitting rustc JSON diagnostics.
     /// May include {label} which will get the label from the `build` section of a crate.
     Flycheck,
+
+    /// For forwards-compatibility, i.e. old rust-analyzer binary with newer workspace discovery tools
+    Unknown,
 }
 
 #[derive(Serialize, Deserialize, Debug, Clone, Eq, PartialEq)]
@@ -478,6 +481,11 @@ pub enum RunnableKindData {
     Check,
     Run,
     TestOne,
+
+    /// For forwards-compatibility, i.e. old rust-analyzer binary with newer workspace discovery tools
+    #[allow(unused)]
+    #[serde(other)]
+    Unknown,
 }
 
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Deserialize, Serialize)]
@@ -546,6 +554,7 @@ impl From<RunnableKindData> for RunnableKind {
             RunnableKindData::Run => RunnableKind::Run,
             RunnableKindData::TestOne => RunnableKind::TestOne,
             RunnableKindData::Flycheck => RunnableKind::Flycheck,
+            RunnableKindData::Unknown => RunnableKind::Unknown,
         }
     }
 }
diff --git a/crates/project-model/test_data/labeled-project.json b/crates/project-model/test_data/labeled-project.json
index 50f66739cf..5c0e1f3397 100644
--- a/crates/project-model/test_data/labeled-project.json
+++ b/crates/project-model/test_data/labeled-project.json
@@ -26,6 +26,12 @@
             "program": "$ROOT$custom-flychecker.sh",
             "args": ["{label}"],
             "cwd": "$ROOT$"
+        },
+        {
+            "kind": "we-ignore-unknown-runnable-kinds-for-forwards-compatibility",
+            "program": "abc",
+            "args": ["{label}"],
+            "cwd": "$ROOT$"
         }
     ]
 }