diff --git a/include/tensor.hpp b/include/tensor.hpp
index 3b329c0..d72c6db 100644
--- a/include/tensor.hpp
+++ b/include/tensor.hpp
@@ -16,19 +16,9 @@ enum class DType
     // INT32,  // Not implemented yet
 };
 
-size_t dtype_size(DType dtype) {
-    switch (dtype)
-    {
-    case DType::FLOAT32:
-        return 4;
-        break;
-    
-    default:
-        throw std::runtime_error("Unknown DType");
-        break;
-    }
-}
+size_t dtype_size(DType dtype);
 
+// Forward declaration
 class Backend;
 
 class Tensor
diff --git a/src/tensor.cpp b/src/tensor.cpp
index fbfd2b4..8412370 100644
--- a/src/tensor.cpp
+++ b/src/tensor.cpp
@@ -4,6 +4,19 @@
 
 using namespace CUDANet;
 
+size_t dtype_size(DType dtype) {
+    switch (dtype)
+    {
+    case DType::FLOAT32:
+        return 4;
+        break;
+    
+    default:
+        throw std::runtime_error("Unknown DType");
+        break;
+    }
+}
+
 Tensor::Tensor(Shape shape, CUDANet::Backend* backend)
     : Tensor(shape, backend->get_default_dtype(), backend) {}