diff --git a/.gitmodules b/.gitmodules
index bf9bdd9a5b4b..6274efaec6c0 100644
--- a/.gitmodules
+++ b/.gitmodules
@@ -43,7 +43,7 @@
 	url = https://github.com/rust-lang/rust-by-example.git
 [submodule "src/llvm-emscripten"]
 	path = src/llvm-emscripten
-	url = https://github.com/rust-lang/llvm.git
+	url = https://github.com/kripken/emscripten-fastcomp
 [submodule "src/stdsimd"]
 	path = src/stdsimd
 	url = https://github.com/rust-lang-nursery/stdsimd.git
diff --git a/src/bootstrap/compile.rs b/src/bootstrap/compile.rs
index 885ad07e0873..cef0849937bf 100644
--- a/src/bootstrap/compile.rs
+++ b/src/bootstrap/compile.rs
@@ -736,7 +736,7 @@ pub fn build_codegen_backend(builder: &Builder,
 
             // Pass down configuration from the LLVM build into the build of
             // librustc_llvm and librustc_codegen_llvm.
-            if builder.is_rust_llvm(target) {
+            if builder.is_rust_llvm(target) && backend != "emscripten" {
                 cargo.env("LLVM_RUSTLLVM", "1");
             }
             cargo.env("LLVM_CONFIG", &llvm_config);
diff --git a/src/ci/docker/asmjs/Dockerfile b/src/ci/docker/asmjs/Dockerfile
index cb85cf3d9e9f..9eaffbf83eb4 100644
--- a/src/ci/docker/asmjs/Dockerfile
+++ b/src/ci/docker/asmjs/Dockerfile
@@ -20,11 +20,11 @@ COPY scripts/sccache.sh /scripts/
 RUN sh /scripts/sccache.sh
 
 ENV PATH=$PATH:/emsdk-portable
-ENV PATH=$PATH:/emsdk-portable/clang/e1.37.13_64bit/
-ENV PATH=$PATH:/emsdk-portable/emscripten/1.37.13/
-ENV PATH=$PATH:/emsdk-portable/node/4.1.1_64bit/bin/
-ENV EMSCRIPTEN=/emsdk-portable/emscripten/1.37.13/
-ENV BINARYEN_ROOT=/emsdk-portable/clang/e1.37.13_64bit/binaryen/
+ENV PATH=$PATH:/emsdk-portable/clang/e1.38.15_64bit/
+ENV PATH=$PATH:/emsdk-portable/emscripten/1.38.15/
+ENV PATH=$PATH:/emsdk-portable/node/8.9.1_64bit/bin/
+ENV EMSCRIPTEN=/emsdk-portable/emscripten/1.38.15/
+ENV BINARYEN_ROOT=/emsdk-portable/clang/e1.38.15_64bit/binaryen/
 ENV EM_CONFIG=/emsdk-portable/.emscripten
 
 ENV TARGETS=asmjs-unknown-emscripten
diff --git a/src/ci/docker/scripts/emscripten.sh b/src/ci/docker/scripts/emscripten.sh
index d32ed6b461d8..dc4b2af792cf 100644
--- a/src/ci/docker/scripts/emscripten.sh
+++ b/src/ci/docker/scripts/emscripten.sh
@@ -33,8 +33,8 @@ curl -fL https://s3.amazonaws.com/mozilla-games/emscripten/releases/emsdk-portab
 
 cd /emsdk-portable
 ./emsdk update
-hide_output ./emsdk install sdk-1.37.13-64bit
-./emsdk activate sdk-1.37.13-64bit
+hide_output ./emsdk install sdk-1.38.15-64bit
+./emsdk activate sdk-1.38.15-64bit
 
 # Compile and cache libc
 source ./emsdk_env.sh
diff --git a/src/llvm-emscripten b/src/llvm-emscripten
index 271744475331..272d3ff91b38 160000
--- a/src/llvm-emscripten
+++ b/src/llvm-emscripten
@@ -1 +1 @@
-Subproject commit 2717444753318e461e0c3b30dacd03ffbac96903
+Subproject commit 272d3ff91b38eac051bdbaf6cf84db5c901ce2f8
diff --git a/src/rustllvm/PassWrapper.cpp b/src/rustllvm/PassWrapper.cpp
index 06f75d981e3d..902e62ab4a1d 100644
--- a/src/rustllvm/PassWrapper.cpp
+++ b/src/rustllvm/PassWrapper.cpp
@@ -444,7 +444,7 @@ extern "C" void LLVMRustConfigurePassManagerBuilder(
     LLVMPassManagerBuilderRef PMBR, LLVMRustCodeGenOptLevel OptLevel,
     bool MergeFunctions, bool SLPVectorize, bool LoopVectorize, bool PrepareForThinLTO,
     const char* PGOGenPath, const char* PGOUsePath) {
-#if LLVM_RUSTLLVM
+#if LLVM_VERSION_GE(7, 0)
   unwrap(PMBR)->MergeFunctions = MergeFunctions;
 #endif
   unwrap(PMBR)->SLPVectorize = SLPVectorize;