diff --git a/.github/workflows/ubuntu.yml b/.github/workflows/ubuntu.yml
index 7f5fe71f7..d09b640fe 100644
--- a/.github/workflows/ubuntu.yml
+++ b/.github/workflows/ubuntu.yml
@@ -118,6 +118,16 @@ jobs:
       - name: build
         run: cmake --build build --target ci_test_amalgamation
 
+  ci_test_diagnostics:
+    runs-on: ubuntu-latest
+    container: nlohmann/json-ci:latest
+    steps:
+      - uses: actions/checkout@v2
+      - name: cmake
+        run: cmake -S . -B build -DJSON_CI=On
+      - name: build
+        run: cmake --build build --target ci_test_diagnostics
+
   ci_test_noexceptions:
     runs-on: ubuntu-latest
     container: nlohmann/json-ci:latest
diff --git a/cmake/ci.cmake b/cmake/ci.cmake
index bd0261d58..5085c369d 100644
--- a/cmake/ci.cmake
+++ b/cmake/ci.cmake
@@ -431,7 +431,7 @@ add_custom_target(ci_test_noexceptions
     -S${PROJECT_SOURCE_DIR} -B${PROJECT_BINARY_DIR}/build_noexceptions
     COMMAND ${CMAKE_COMMAND} --build ${PROJECT_BINARY_DIR}/build_noexceptions
     COMMAND cd ${PROJECT_BINARY_DIR}/build_noexceptions && ${CMAKE_CTEST_COMMAND} --parallel ${N} --output-on-failure
-    COMMENT "Compile and test with with exceptions switched off"
+    COMMENT "Compile and test with exceptions switched off"
 )
 
 ###############################################################################
@@ -445,7 +445,21 @@ add_custom_target(ci_test_noimplicitconversions
     -S${PROJECT_SOURCE_DIR} -B${PROJECT_BINARY_DIR}/build_noimplicitconversions
     COMMAND ${CMAKE_COMMAND} --build ${PROJECT_BINARY_DIR}/build_noimplicitconversions
     COMMAND cd ${PROJECT_BINARY_DIR}/build_noimplicitconversions && ${CMAKE_CTEST_COMMAND} --parallel ${N} --output-on-failure
-    COMMENT "Compile and test with with implicit conversions switched off"
+    COMMENT "Compile and test with implicit conversions switched off"
+)
+
+###############################################################################
+# Enable improved diagnostics.
+###############################################################################
+
+add_custom_target(ci_test_diagnostics
+    COMMAND CXX=${CLANG_TOOL} ${CMAKE_COMMAND}
+    -DCMAKE_BUILD_TYPE=Debug -GNinja
+    -DJSON_BuildTests=ON -DJSON_MultipleHeaders=ON -DJSON_Diagnostics=ON
+    -S${PROJECT_SOURCE_DIR} -B${PROJECT_BINARY_DIR}/build_diagnostics
+    COMMAND ${CMAKE_COMMAND} --build ${PROJECT_BINARY_DIR}/build_diagnostics
+    COMMAND cd ${PROJECT_BINARY_DIR}/build_diagnostics && ${CMAKE_CTEST_COMMAND} --parallel ${N} --output-on-failure
+    COMMENT "Compile and test with improved diagnostics enabled"
 )
 
 ###############################################################################
@@ -741,7 +755,7 @@ else()
     )
 endif()
 
-set(JSON_CMAKE_FLAGS "JSON_BuildTests;JSON_Install;JSON_MultipleHeaders;JSON_Sanitizer;JSON_Valgrind;JSON_NoExceptions;JSON_Coverage")
+set(JSON_CMAKE_FLAGS "JSON_BuildTests;JSON_Install;JSON_MultipleHeaders;JSON_Sanitizer;JSON_Valgrind;JSON_NoExceptions;JSON_Coverage;JSON_Diagnostics")
 
 foreach(JSON_CMAKE_FLAG ${JSON_CMAKE_FLAGS})
     string(TOLOWER "ci_cmake_flag_${JSON_CMAKE_FLAG}" JSON_CMAKE_FLAG_TARGET)
diff --git a/include/nlohmann/detail/exceptions.hpp b/include/nlohmann/detail/exceptions.hpp
index 74fd048a3..8ad5d123a 100644
--- a/include/nlohmann/detail/exceptions.hpp
+++ b/include/nlohmann/detail/exceptions.hpp
@@ -3,6 +3,7 @@
 #include <exception> // exception
 #include <stdexcept> // runtime_error
 #include <string> // to_string
+#include <vector> // vector
 
 #include <nlohmann/detail/value_t.hpp>
 #include <nlohmann/detail/string_escape.hpp>
@@ -118,6 +119,7 @@ class exception : public std::exception
             return a + "/" + detail::escape(b);
         }) + ") ";
 #else
+        static_cast<void>(leaf_element);
         return "";
 #endif
     }
diff --git a/single_include/nlohmann/json.hpp b/single_include/nlohmann/json.hpp
index 032d1ebd1..c43c5e798 100644
--- a/single_include/nlohmann/json.hpp
+++ b/single_include/nlohmann/json.hpp
@@ -72,6 +72,7 @@ SOFTWARE.
 #include <exception> // exception
 #include <stdexcept> // runtime_error
 #include <string> // to_string
+#include <vector> // vector
 
 // #include <nlohmann/detail/value_t.hpp>
 
@@ -2705,6 +2706,7 @@ class exception : public std::exception
             return a + "/" + detail::escape(b);
         }) + ") ";
 #else
+        static_cast<void>(leaf_element);
         return "";
 #endif
     }