diff --git a/src/Reactor/LLVMReactor.cpp b/src/Reactor/LLVMReactor.cpp
index 2508508..468acc4 100644
--- a/src/Reactor/LLVMReactor.cpp
+++ b/src/Reactor/LLVMReactor.cpp
@@ -3219,6 +3219,15 @@
 		})));
 	}
 
+	RValue<UInt4> Cttz(RValue<UInt4> v, bool isZeroUndef)
+	{
+		auto func = llvm::Intrinsic::getDeclaration(::module, llvm::Intrinsic::cttz, { T(UInt4::getType()), T(Bool::getType()) } );
+		return RValue<UInt4>(V(::builder->CreateCall(func, {
+			V(v.value),
+			isZeroUndef ? ::llvm::ConstantInt::getTrue(*::context) : ::llvm::ConstantInt::getFalse(*::context)
+		})));
+	}
+
 	Type *Float4::getType()
 	{
 		return T(llvm::VectorType::get(T(Float::getType()), 4));
diff --git a/src/Reactor/Reactor.hpp b/src/Reactor/Reactor.hpp
index 69a73ba..1d2b2b0 100644
--- a/src/Reactor/Reactor.hpp
+++ b/src/Reactor/Reactor.hpp
@@ -2238,6 +2238,11 @@
 	// Returns an undefined value when: !isZeroUndef && x == 0.
 	RValue<UInt4> Ctlz(RValue<UInt4> x, bool isZeroUndef);
 
+	// Count trailing zeros.
+	// Returns 32 when: isZeroUndef && x == 0.
+	// Returns an undefined value when: !isZeroUndef && x == 0.
+	RValue<UInt4> Cttz(RValue<UInt4> x, bool isZeroUndef);
+
 	template<class T>
 	class Pointer : public LValue<Pointer<T>>
 	{