diff --git a/1-ProceduralProgramming/3-Types.ipynb b/1-ProceduralProgramming/3-Types.ipynb
index f45dfcbf44d63290ce298b1993638b1d924b564d..38916e9d344e9909b98732b6d3858dbdd79bfb2e 100644
--- a/1-ProceduralProgramming/3-Types.ipynb
+++ b/1-ProceduralProgramming/3-Types.ipynb
@@ -284,6 +284,8 @@
     "\n",
     "The STL features rather heavily a type named `std::size_t`, which by design is able to store the maximum size of a theoretically possible object of any type (including array). On most (all?) systems `std::size_t` is an alias to an `unsigned long`. More may be found about this type on [CppReference](https://en.cppreference.com/w/cpp/types/size_t). The equivalent counter part for signed integers is the [`std::ptrdiff_t`](https://en.cppreference.com/w/cpp/types/ptrdiff_t), which is the signed integer type of the result of subtracting two pointers. \n",
     "\n",
+    "You might also encounter [`std::ptrdiff_t`](https://en.cppreference.com/w/cpp/types/ptrdiff_t), which is akin to `std::size_t` but for *signed* values. It is typically used in the STL to store the result of subtracting two pointers. \n",
+    "\n",
     "\n",
     "#### Numeric limits\n",
     "\n",