diff --git a/integrations/rust-project/src/cli/develop.rs b/integrations/rust-project/src/cli/develop.rs
index d075e9d500fe8..9b1c130b7ee46 100644
--- a/integrations/rust-project/src/cli/develop.rs
+++ b/integrations/rust-project/src/cli/develop.rs
@@ -107,14 +107,27 @@ impl Develop {
         }
 
         if let crate::Command::DevelopJson {
+            sysroot_mode,
             args,
             log_scuba_to_stdout: _,
         } = command
         {
             let out = Output::Stdout;
-            let sysroot = SysrootConfig::BuckConfig;
             let mode = select_mode(None);
 
+            let sysroot = match sysroot_mode {
+                crate::SysrootMode::BuckConfig => SysrootConfig::BuckConfig,
+                crate::SysrootMode::Rustup => SysrootConfig::Rustup,
+                crate::SysrootMode::FullPath(path) => SysrootConfig::Sysroot(path),
+                crate::SysrootMode::Command(cmd_args) => {
+                    let cmd = cmd_args[0].clone();
+                    let args = cmd_args[1..].to_vec();
+                    let output = std::process::Command::new(cmd).args(args).output().unwrap();
+                    let path = String::from_utf8(output.stdout).unwrap();
+                    SysrootConfig::Sysroot(PathBuf::from(path.trim()))
+                }
+            };
+
             let buck = buck::Buck::new(mode);
 
             let develop = Develop {
diff --git a/integrations/rust-project/src/main.rs b/integrations/rust-project/src/main.rs
index afb4b12f79ba9..9b1bd80370a28 100644
--- a/integrations/rust-project/src/main.rs
+++ b/integrations/rust-project/src/main.rs
@@ -120,6 +120,16 @@ enum Command {
         #[clap(long, hide = true)]
         log_scuba_to_stdout: bool,
 
+        // FIXME XXX: remove this after everything in fbcode is migrated off
+        // of buckconfig implicitly.
+        #[cfg(fbcode_build)]
+        #[clap(long, default_value = "buckconfig")]
+        sysroot_mode: SysrootMode,
+
+        #[cfg(not(fbcode_build))]
+        #[clap(long, default_value = "rustup")]
+        sysroot_mode: SysrootMode,
+
         args: JsonArguments,
     },
     /// Build the saved file's owning target. This is meant to be used by IDEs to provide diagnostics on save.
@@ -137,6 +147,43 @@ enum Command {
     },
 }
 
+/// The 'develop-json' command needs to have 3 modes:
+/// 1. Static `.buckconfig` setting
+/// 2. Absolute path setting
+/// 3. Use `rustc --print=sysroot` ("rustup mode")
+/// 4. Run a command and take the output from stdout
+#[derive(PartialEq, Clone, Debug, Deserialize)]
+enum SysrootMode {
+    Rustup,
+    Command(Vec<String>),
+    FullPath(PathBuf),
+    BuckConfig,
+}
+
+impl FromStr for SysrootMode {
+    type Err = anyhow::Error;
+
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        if s == "rustup" {
+            Ok(SysrootMode::Rustup)
+        } else if s == "buckconfig" {
+            Ok(SysrootMode::BuckConfig)
+        } else if s.starts_with("path:") {
+            let s = s.trim_start_matches("path:");
+            Ok(SysrootMode::FullPath(PathBuf::from(s)))
+        } else if s.starts_with("cmd:") {
+            let s = s.trim_start_matches("cmd:");
+            Ok(SysrootMode::Command(
+                s.split_whitespace()
+                    .map(|s| s.to_owned())
+                    .collect::<Vec<String>>(),
+            ))
+        } else {
+            Err(anyhow::anyhow!("Invalid mode: {}", s))
+        }
+    }
+}
+
 #[derive(PartialEq, Clone, Debug, Deserialize)]
 #[serde(rename_all = "camelCase")]
 enum JsonArguments {
@@ -325,6 +372,7 @@ fn json_args_pass() {
     let expected = Opt {
         command: Some(Command::DevelopJson {
             args,
+            sysroot_mode: SysrootMode::Rustup,
             log_scuba_to_stdout: false,
         }),
         version: false,
@@ -341,6 +389,7 @@ fn json_args_pass() {
     let expected = Opt {
         command: Some(Command::DevelopJson {
             args,
+            sysroot_mode: SysrootMode::Rustup,
             log_scuba_to_stdout: false,
         }),
         version: false,
@@ -357,6 +406,7 @@ fn json_args_pass() {
     let expected = Opt {
         command: Some(Command::DevelopJson {
             args,
+            sysroot_mode: SysrootMode::Rustup,
             log_scuba_to_stdout: false,
         }),
         version: false,