diff --git a/mk/main.mk b/mk/main.mk
index cc843add50d..e68a8f30055 100644
--- a/mk/main.mk
+++ b/mk/main.mk
@@ -300,7 +300,7 @@ endif
 # LLVM macros
 ######################################################################
 
-LLVM_OPTIONAL_COMPONENTS=x86 arm aarch64 mips powerpc pnacl systemz
+LLVM_OPTIONAL_COMPONENTS=x86 arm aarch64 mips powerpc pnacl systemz jsbackend
 LLVM_REQUIRED_COMPONENTS=ipo bitreader bitwriter linker asmparser mcjit \
                 interpreter instrumentation
 
diff --git a/src/librustc_llvm/build.rs b/src/librustc_llvm/build.rs
index 3f551476e2b..c805fd7c7b6 100644
--- a/src/librustc_llvm/build.rs
+++ b/src/librustc_llvm/build.rs
@@ -66,7 +66,7 @@ fn main() {
     let host = env::var("HOST").expect("HOST was not set");
     let is_crossed = target != host;
 
-    let optional_components = ["x86", "arm", "aarch64", "mips", "powerpc", "pnacl", "systemz"];
+    let optional_components = ["x86", "arm", "aarch64", "mips", "powerpc", "pnacl", "systemz", "jsbackend"];
 
     // FIXME: surely we don't need all these components, right? Stuff like mcjit
     //        or interpreter the compiler itself never uses.