diff --git a/docs/interface.md b/docs/interface.md
index 13a5f7a..5137a92 100644
--- a/docs/interface.md
+++ b/docs/interface.md
@@ -77,6 +77,8 @@
 * uint16
 * ...
 * uint64
+* size - maps to the C 'size_t' for the architecture.
+* ssize - maps to the C 'ssize_t' for the architecture.
 * double
 * unixfd
 * string
diff --git a/test/server/Test.interface.yaml b/test/server/Test.interface.yaml
index 7daea7d..2f86d70 100644
--- a/test/server/Test.interface.yaml
+++ b/test/server/Test.interface.yaml
@@ -12,3 +12,5 @@
       type: int64
       flags:
           - const
+    - name: Countable
+      type: size
diff --git a/tools/sdbusplus/property.py b/tools/sdbusplus/property.py
index e62dc90..2f0ce57 100644
--- a/tools/sdbusplus/property.py
+++ b/tools/sdbusplus/property.py
@@ -123,6 +123,8 @@
             'uint32': {'cppName': 'uint32_t', 'params': 0},
             'int64': {'cppName': 'int64_t', 'params': 0},
             'uint64': {'cppName': 'uint64_t', 'params': 0},
+            'size': {'cppName': 'size_t', 'params': 0},
+            'ssize': {'cppName': 'ssize_t', 'params': 0},
             'double': {'cppName': 'double', 'params': 0},
             'unixfd': {'cppName': 'sdbusplus::message::unix_fd', 'params': 0},
             'string': {'cppName': 'std::string', 'params': 0},