diff --git a/README.md b/README.md
index dee3fb7e8e7a0d3a120ed8d2b3ea92282b51ba74..4d897a4c7e45249f5b1a21d59555c47663203a82 100644
--- a/README.md
+++ b/README.md
@@ -857,7 +857,7 @@ $ make json_unit -Ctest
 $ ./test/json_unit "*""
 
 ===============================================================================
-All tests passed (11202588 assertions in 47 test cases)
+All tests passed (11202596 assertions in 47 test cases)
 ```
 
 Alternatively, you can use [CMake](https://cmake.org) and run
diff --git a/src/json.hpp b/src/json.hpp
index ae01cd3a01d8b53b1b8de381a804877b7b07bc74..6fcfc3e12c1677b92e4c22fb8353a80dbc173db9 100644
--- a/src/json.hpp
+++ b/src/json.hpp
@@ -8315,7 +8315,7 @@ class basic_json
             // negative value indicates an error
             assert(written_bytes > 0);
             // check if buffer was large enough
-            assert(written_bytes < m_buf.size());
+            assert(static_cast<size_t>(written_bytes) < m_buf.size());
 
             // read information from locale
             const auto loc = localeconv();
diff --git a/src/json.hpp.re2c b/src/json.hpp.re2c
index 87a50c7019b7b907d3ffb86003b615d7989649b4..a33da4b3d7fd8685818762d80502bd70ee1e6988 100644
--- a/src/json.hpp.re2c
+++ b/src/json.hpp.re2c
@@ -8315,7 +8315,7 @@ class basic_json
             // negative value indicates an error
             assert(written_bytes > 0);
             // check if buffer was large enough
-            assert(written_bytes < m_buf.size());
+            assert(static_cast<size_t>(written_bytes) < m_buf.size());
 
             // read information from locale
             const auto loc = localeconv();