diff --git a/include/etl/version.h b/include/etl/version.h
index 088f6bdc..93d64b4a 100644
--- a/include/etl/version.h
+++ b/include/etl/version.h
@@ -39,7 +39,7 @@ SOFTWARE.
 
 #define ETL_VERSION_MAJOR 18
 #define ETL_VERSION_MINOR 12
-#define ETL_VERSION_PATCH  3
+#define ETL_VERSION_PATCH  4
 #define ETL_VERSION       ETL_STRINGIFY(ETL_VERSION_MAJOR) "." ETL_STRINGIFY(ETL_VERSION_MINOR) "." ETL_STRINGIFY(ETL_VERSION_PATCH)
 #define ETL_VERSION_W     ETL_STRINGIFY(ETL_VERSION_MAJOR) L"." ETL_STRINGIFY(ETL_VERSION_MINOR) L"." ETL_STRINGIFY(ETL_VERSION_PATCH)
 #define ETL_VERSION_U16   ETL_STRINGIFY(ETL_VERSION_MAJOR) u"." ETL_STRINGIFY(ETL_VERSION_MINOR) u"." ETL_STRINGIFY(ETL_VERSION_PATCH)
diff --git a/library.json b/library.json
index 1f10047b..ad2a269f 100644
--- a/library.json
+++ b/library.json
@@ -1,6 +1,6 @@
 {
   "name": "Embedded Template Library",
-  "version": "18.12.3",
+  "version": "18.12.4",
   "authors": {
     "name": "John Wellbelove",
     "email": "john.wellbelove@etlcpp.com"
diff --git a/library.properties b/library.properties
index 4a136a6d..f28974df 100644
--- a/library.properties
+++ b/library.properties
@@ -1,5 +1,5 @@
 name=Embedded Template Library
-version=18.12.3
+version=18.12.4
 author= John Wellbelove <john.wellbelove@etlcpp.com>
 maintainer=John Wellbelove <john.wellbelove@etlcpp.com>
 license=MIT
diff --git a/support/Release notes.txt b/support/Release notes.txt
index 8d735e4f..6e7cfa7d 100644
--- a/support/Release notes.txt	
+++ b/support/Release notes.txt	
@@ -1,3 +1,7 @@
+===============================================================================
+18.12.4
+Resolve clang 9 compatibility issues.
+
 ===============================================================================
 18.12.3
 Resolve 0U constant ambiguity in string utility tests
diff --git a/test/test_deque.cpp b/test/test_deque.cpp
index a7000d8c..876aa4ea 100644
--- a/test/test_deque.cpp
+++ b/test/test_deque.cpp
@@ -533,14 +533,39 @@ namespace
     {
       DataNDC data(SIZE, N0);
 
-      DataNDC::iterator first = data.begin() + 1;
-      DataNDC::iterator second = data.begin() + 4;
+      DataNDC::iterator first  = data.begin() + 1;
+      DataNDC::iterator second = data.begin() + 1;
+      DataNDC::iterator third  = data.begin() + 4;
 
-      CHECK(first < second);
+      CHECK(first    == second);
+      CHECK(second   == first);
+      CHECK(!(first  == third));
+      CHECK(!(third  == first));
+
+      CHECK(!(first  != second));
+      CHECK(!(second != first));
+      CHECK(first    != third);
+      CHECK(third    != first);
+
+      CHECK(!(first  < second));
       CHECK(!(second < first));
+      CHECK(first    < third);
+      CHECK(!(third  < first));
 
-      CHECK(second > first);
-      CHECK(!(first > second));
+      CHECK(first    <= second);
+      CHECK(second   <= first);
+      CHECK(first    <= third);
+      CHECK(!(third  <= first));
+
+      CHECK(!(first  > second));
+      CHECK(!(second > first));
+      CHECK(!(first  > third));
+      CHECK(third    > first);
+
+      CHECK(first    >= second);
+      CHECK(second   >= first);
+      CHECK(!(first  >= third));
+      CHECK(third    >= first);
     }
 
     //*************************************************************************
@@ -548,14 +573,39 @@ namespace
     {
       DataNDC data(SIZE, N0);
 
-      DataNDC::const_iterator first  = data.cbegin() + 1;
-      DataNDC::const_iterator second = data.cbegin() + 4;
+      DataNDC::const_iterator first  = data.begin() + 1;
+      DataNDC::const_iterator second = data.begin() + 1;
+      DataNDC::const_iterator third  = data.begin() + 4;
 
-      CHECK(first < second);
+      CHECK(first    == second);
+      CHECK(second   == first);
+      CHECK(!(first  == third));
+      CHECK(!(third  == first));
+
+      CHECK(!(first  != second));
+      CHECK(!(second != first));
+      CHECK(first    != third);
+      CHECK(third    != first);
+
+      CHECK(!(first  < second));
       CHECK(!(second < first));
+      CHECK(first    < third);
+      CHECK(!(third  < first));
 
-      CHECK(second > first);
-      CHECK(!(first > second));
+      CHECK(first    <= second);
+      CHECK(second   <= first);
+      CHECK(first    <= third);
+      CHECK(!(third  <= first));
+
+      CHECK(!(first  > second));
+      CHECK(!(second > first));
+      CHECK(!(first  > third));
+      CHECK(third    > first);
+
+      CHECK(first    >= second);
+      CHECK(second   >= first);
+      CHECK(!(first  >= third));
+      CHECK(third    >= first);
     }
 
     //*************************************************************************