diff --git a/README.md b/README.md
index a29879a..2d9f2fc 100644
--- a/README.md
+++ b/README.md
@@ -118,7 +118,7 @@ int main()
     }
 
     // Checking if the destination is the RCX register.
-    if (ND_IS_OP_REG(&ix.Operands[0], ND_REG_GPR, 8, REG_RCX))
+    if (ND_IS_OP_REG(&ix.Operands[0], ND_REG_GPR, 8, NDR_RCX))
     {
         printf("The first op is RCX!\n");
     }
diff --git a/docs/source/index.rst b/docs/source/index.rst
index 5e1d1e1..e73b52d 100644
--- a/docs/source/index.rst
+++ b/docs/source/index.rst
@@ -267,7 +267,7 @@ Determining if the first operand is register EAX
 .. code-block:: c
    :linenos:
    
-   if (ND_IS_OP_REG(&ix.Operands[0], ND_REG_GPR, 4, REG_EAX))
+   if (ND_IS_OP_REG(&ix.Operands[0], ND_REG_GPR, 4, NDR_EAX))
    
 Determining if the second operand is the stack
 ----------------------------------------------