diff --git a/src/bootstrap/config.rs b/src/bootstrap/config.rs
index abad216d89be4..edbd61d8eb21e 100644
--- a/src/bootstrap/config.rs
+++ b/src/bootstrap/config.rs
@@ -59,6 +59,7 @@ pub struct Config {
     pub llvm_static_stdcpp: bool,
     pub llvm_link_shared: bool,
     pub llvm_targets: Option<String>,
+    pub llvm_experimental_targets: Option<String>,
     pub llvm_link_jobs: Option<u32>,
     pub llvm_clean_rebuild: bool,
 
@@ -187,6 +188,7 @@ struct Llvm {
     version_check: Option<bool>,
     static_libstdcpp: Option<bool>,
     targets: Option<String>,
+    experimental_targets: Option<String>,
     link_jobs: Option<u32>,
     clean_rebuild: Option<bool>,
 }
@@ -347,6 +349,7 @@ impl Config {
             set(&mut config.llvm_static_stdcpp, llvm.static_libstdcpp);
             set(&mut config.llvm_clean_rebuild, llvm.clean_rebuild);
             config.llvm_targets = llvm.targets.clone();
+            config.llvm_experimental_targets = llvm.experimental_targets.clone();
             config.llvm_link_jobs = llvm.link_jobs;
         }
 
diff --git a/src/bootstrap/config.toml.example b/src/bootstrap/config.toml.example
index 0eb6c4c82c4dd..536c5129b3986 100644
--- a/src/bootstrap/config.toml.example
+++ b/src/bootstrap/config.toml.example
@@ -51,7 +51,12 @@
 # support. You'll need to write a target specification at least, and most
 # likely, teach rustc about the C ABI of the target. Get in touch with the
 # Rust team and file an issue if you need assistance in porting!
-#targets = "X86;ARM;AArch64;Mips;PowerPC;SystemZ;JSBackend;MSP430;Sparc;NVPTX;Hexagon"
+#targets = "X86;ARM;AArch64;Mips;PowerPC;SystemZ;JSBackend;MSP430;Sparc"
+
+# Experimental LLVM targets to build supoort for. These are specified in the
+# same format as the normal targets, but are different in that they need be
+# opted into. The available targets are NVPTX and Hexagon.
+#experimental-targets = ""
 
 # Cap the number of parallel linker invocations when compiling LLVM.
 # This can be useful when building LLVM with debug info, which significantly
diff --git a/src/bootstrap/native.rs b/src/bootstrap/native.rs
index 6b9a6347d2272..0c28308136f5b 100644
--- a/src/bootstrap/native.rs
+++ b/src/bootstrap/native.rs
@@ -83,7 +83,12 @@ pub fn llvm(build: &Build, target: &str) {
     // NOTE: remember to also update `config.toml.example` when changing the defaults!
     let llvm_targets = match build.config.llvm_targets {
         Some(ref s) => s,
-        None => "X86;ARM;AArch64;Mips;PowerPC;SystemZ;JSBackend;MSP430;Sparc;NVPTX;Hexagon",
+        None => "X86;ARM;AArch64;Mips;PowerPC;SystemZ;JSBackend;MSP430;Sparc",
+    };
+
+    let llvm_exp_targets = match build.config.llvm_experimental_targets {
+        Some(ref s) => s,
+        None => "",
     };
 
     let assertions = if build.config.llvm_assertions {"ON"} else {"OFF"};
@@ -94,6 +99,7 @@ pub fn llvm(build: &Build, target: &str) {
        .profile(profile)
        .define("LLVM_ENABLE_ASSERTIONS", assertions)
        .define("LLVM_TARGETS_TO_BUILD", llvm_targets)
+       .define("LLVM_EXPERIMENTAL_TARGETS_TO_BUILD", llvm_exp_targets)
        .define("LLVM_INCLUDE_EXAMPLES", "OFF")
        .define("LLVM_INCLUDE_TESTS", "OFF")
        .define("LLVM_INCLUDE_DOCS", "OFF")