diff --git a/src/Pipeline/SpirvShader.cpp b/src/Pipeline/SpirvShader.cpp
index ab12f60..14fcc0a 100644
--- a/src/Pipeline/SpirvShader.cpp
+++ b/src/Pipeline/SpirvShader.cpp
@@ -3329,6 +3329,16 @@
 			}
 			break;
 		}
+		case GLSLstd450Atan:
+		{
+			auto val = GenericValue(this, routine, insn.word(5));
+			for (auto i = 0u; i < type.sizeInComponents; i++)
+			{
+				dst.move(i, Atan(val.Float(i)));
+			}
+			break;
+		}
+
 		default:
 			UNIMPLEMENTED("Unhandled ExtInst %d", extInstIndex);
 		}
diff --git a/src/Reactor/LLVMReactor.cpp b/src/Reactor/LLVMReactor.cpp
index d3fd354..5a3f5f6 100644
--- a/src/Reactor/LLVMReactor.cpp
+++ b/src/Reactor/LLVMReactor.cpp
@@ -558,6 +558,7 @@
 			func_.emplace("cosf", reinterpret_cast<void*>(cosf));
 			func_.emplace("asinf", reinterpret_cast<void*>(asinf));
 			func_.emplace("acosf", reinterpret_cast<void*>(acosf));
+			func_.emplace("atanf", reinterpret_cast<void*>(atanf));
 
 #ifdef __APPLE__
 			// LLVM uses this function on macOS for tan.
@@ -3114,6 +3115,11 @@
 		return TransformFloat4PerElement(v, "acosf");
 	}
 
+	RValue<Float4> Atan(RValue<Float4> v)
+	{
+		return TransformFloat4PerElement(v, "atanf");
+	}
+
 	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 96c87e0..d9eb3e6 100644
--- a/src/Reactor/Reactor.hpp
+++ b/src/Reactor/Reactor.hpp
@@ -2213,6 +2213,7 @@
 	RValue<Float4> Tan(RValue<Float4> x);
 	RValue<Float4> Asin(RValue<Float4> x);
 	RValue<Float4> Acos(RValue<Float4> x);
+	RValue<Float4> Atan(RValue<Float4> x);
 
 	template<class T>
 	class Pointer : public LValue<Pointer<T>>