diff --git a/src/librustc_trans/trans/context.rs b/src/librustc_trans/trans/context.rs
index 10edb72f0e200..a39ab4978edb3 100644
--- a/src/librustc_trans/trans/context.rs
+++ b/src/librustc_trans/trans/context.rs
@@ -873,14 +873,12 @@ fn declare_intrinsic(ccx: &CrateContext, key: & &'static str) -> Option<ValueRef
     ifn!("llvm.lifetime.end", fn(t_i64, i8p) -> void);
 
     ifn!("llvm.expect.i1", fn(i1, i1) -> i1);
-    ifn!("llvm.assume", fn(i1) -> void);
 
     // Some intrinsics were introduced in later versions of LLVM, but they have
-    // fallbacks in libc or libm and such. Currently, all of these intrinsics
-    // were introduced in LLVM 3.4, so we case on that.
+    // fallbacks in libc or libm and such.
     macro_rules! compatible_ifn {
-        ($name:expr, $cname:ident ($($arg:expr),*) -> $ret:expr) => (
-            if unsafe { llvm::LLVMVersionMinor() >= 4 } {
+        ($name:expr, $cname:ident ($($arg:expr),*) -> $ret:expr, $llvm_version:expr) => (
+            if unsafe { llvm::LLVMVersionMinor() >= $llvm_version } {
                 // The `if key == $name` is already in ifn!
                 ifn!($name, fn($($arg),*) -> $ret);
             } else if *key == $name {
@@ -893,10 +891,11 @@ fn declare_intrinsic(ccx: &CrateContext, key: & &'static str) -> Option<ValueRef
         )
     }
 
-    compatible_ifn!("llvm.copysign.f32", copysignf(t_f32, t_f32) -> t_f32);
-    compatible_ifn!("llvm.copysign.f64", copysign(t_f64, t_f64) -> t_f64);
-    compatible_ifn!("llvm.round.f32", roundf(t_f32) -> t_f32);
-    compatible_ifn!("llvm.round.f64", round(t_f64) -> t_f64);
+    compatible_ifn!("llvm.copysign.f32", copysignf(t_f32, t_f32) -> t_f32, 4);
+    compatible_ifn!("llvm.copysign.f64", copysign(t_f64, t_f64) -> t_f64, 4);
+    compatible_ifn!("llvm.round.f32", roundf(t_f32) -> t_f32, 4);
+    compatible_ifn!("llvm.round.f64", round(t_f64) -> t_f64, 4);
+    compatible_ifn!("llvm.assume", llvmcompat_assume(i1) -> void, 6);
 
 
     if ccx.sess().opts.debuginfo != NoDebugInfo {
diff --git a/src/rt/rust_builtin.c b/src/rt/rust_builtin.c
index 03cd3fd6b88ea..8bf184770b48f 100644
--- a/src/rt/rust_builtin.c
+++ b/src/rt/rust_builtin.c
@@ -13,6 +13,7 @@
 #include <string.h>
 #include <assert.h>
 #include <stdlib.h>
+#include <stdbool.h>
 
 #if !defined(__WIN32__)
 #include <sys/time.h>
@@ -199,6 +200,11 @@ rust_unset_sigprocmask() {
 int *__dfly_error(void) { return __error(); }
 #endif
 
+void
+llvmcompat_assume(bool c) {
+    // empty stub for LLVM before 3.6
+}
+
 //
 // Local Variables:
 // mode: C++
diff --git a/src/rustllvm/ExecutionEngineWrapper.cpp b/src/rustllvm/ExecutionEngineWrapper.cpp
index d37cf9d12a5e0..2a8b2aa25a8fc 100644
--- a/src/rustllvm/ExecutionEngineWrapper.cpp
+++ b/src/rustllvm/ExecutionEngineWrapper.cpp
@@ -82,7 +82,6 @@ extern "C" LLVMExecutionEngineRef LLVMBuildExecutionEngine(
     InitializeNativeTargetAsmPrinter();
     InitializeNativeTargetAsmParser();
 
-    std::unique_ptr<Module> m(unwrap(mod));
     RustJITMemoryManager *mm = unwrap(mref);
 
     std::string error_str;
@@ -91,12 +90,22 @@ extern "C" LLVMExecutionEngineRef LLVMBuildExecutionEngine(
     options.JITEmitDebugInfo = true;
     options.NoFramePointerElim = true;
 
+#if LLVM_VERSION_MINOR > 5
+    std::unique_ptr<Module> m(unwrap(mod));
     ExecutionEngine *ee = EngineBuilder(std::move(m))
         .setEngineKind(EngineKind::JIT)
         .setErrorStr(&error_str)
         .setMCJITMemoryManager(mm)
         .setTargetOptions(options)
         .create();
+#else
+    ExecutionEngine *ee = EngineBuilder(unwrap(mod))
+        .setEngineKind(EngineKind::JIT)
+        .setErrorStr(&error_str)
+        .setMCJITMemoryManager(mm)
+        .setTargetOptions(options)
+        .create();
+#endif
 
     if (!ee)
         LLVMRustSetLastError(error_str.c_str());