diff --git a/applications/utilities/mesh/conversion/ansysToFoam/ansysToFoam.L b/applications/utilities/mesh/conversion/ansysToFoam/ansysToFoam.L
index c3d443d2fe..ead8621bc7 100644
--- a/applications/utilities/mesh/conversion/ansysToFoam/ansysToFoam.L
+++ b/applications/utilities/mesh/conversion/ansysToFoam/ansysToFoam.L
@@ -58,7 +58,7 @@ Description
 #include "SLPtrList.H"
 
 // Flex may use register, which is deprecated and incompatible with C++17
-#pragma GCC diagnostic ignored "-Wdeprecated-register"
+#pragma clang diagnostic ignored "-Wdeprecated-register"
 
 using namespace Foam;
 
diff --git a/applications/utilities/mesh/conversion/fluent3DMeshToFoam/fluent3DMeshToFoam.L b/applications/utilities/mesh/conversion/fluent3DMeshToFoam/fluent3DMeshToFoam.L
index 9e28c08886..69fd78f75d 100644
--- a/applications/utilities/mesh/conversion/fluent3DMeshToFoam/fluent3DMeshToFoam.L
+++ b/applications/utilities/mesh/conversion/fluent3DMeshToFoam/fluent3DMeshToFoam.L
@@ -53,7 +53,7 @@ Description
 #include "readHexLabel.H"
 
 // Flex may use register, which is deprecated and incompatible with C++17
-#pragma GCC diagnostic ignored "-Wdeprecated-register"
+#pragma clang diagnostic ignored "-Wdeprecated-register"
 
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 
diff --git a/applications/utilities/mesh/conversion/fluentMeshToFoam/fluentMeshToFoam.L b/applications/utilities/mesh/conversion/fluentMeshToFoam/fluentMeshToFoam.L
index 96c7c84b1a..447fd88c72 100644
--- a/applications/utilities/mesh/conversion/fluentMeshToFoam/fluentMeshToFoam.L
+++ b/applications/utilities/mesh/conversion/fluentMeshToFoam/fluentMeshToFoam.L
@@ -59,7 +59,7 @@ Description
 #include "repatchPolyTopoChanger.H"
 
 // Flex may use register, which is deprecated and incompatible with C++17
-#pragma GCC diagnostic ignored "-Wdeprecated-register"
+#pragma clang diagnostic ignored "-Wdeprecated-register"
 
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 
diff --git a/applications/utilities/mesh/conversion/gambitToFoam/gambitToFoam.L b/applications/utilities/mesh/conversion/gambitToFoam/gambitToFoam.L
index 280964986d..a030875180 100644
--- a/applications/utilities/mesh/conversion/gambitToFoam/gambitToFoam.L
+++ b/applications/utilities/mesh/conversion/gambitToFoam/gambitToFoam.L
@@ -47,7 +47,7 @@ Description
 #include <cstdio>
 
 // Flex may use register, which is deprecated and incompatible with C++17
-#pragma GCC diagnostic ignored "-Wdeprecated-register"
+#pragma clang diagnostic ignored "-Wdeprecated-register"
 
 using namespace Foam;
 
diff --git a/src/fileFormats/stl/STLReaderASCII.L b/src/fileFormats/stl/STLReaderASCII.L
index 1915bad978..1b031bf6a9 100644
--- a/src/fileFormats/stl/STLReaderASCII.L
+++ b/src/fileFormats/stl/STLReaderASCII.L
@@ -37,7 +37,7 @@ License
 #include "OSspecific.H"
 
 // Flex may use register, which is deprecated and incompatible with C++17
-#pragma GCC diagnostic ignored "-Wdeprecated-register"
+#pragma clang diagnostic ignored "-Wdeprecated-register"
 
 using namespace Foam;
 // Dummy yyFlexLexer::yylex() to keep the linker happy. It is not called
diff --git a/src/thermophysicalModels/reactionThermo/chemistryReaders/chemkinReader/chemkinLexer.L b/src/thermophysicalModels/reactionThermo/chemistryReaders/chemkinReader/chemkinLexer.L
index 38966b6d41..9db567ba47 100644
--- a/src/thermophysicalModels/reactionThermo/chemistryReaders/chemkinReader/chemkinLexer.L
+++ b/src/thermophysicalModels/reactionThermo/chemistryReaders/chemkinReader/chemkinLexer.L
@@ -35,7 +35,7 @@ License
 #include <cstdio>
 
 // Flex may use register, which is deprecated and incompatible with C++17
-#pragma GCC diagnostic ignored "-Wdeprecated-register"
+#pragma clang diagnostic ignored "-Wdeprecated-register"
 
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 
diff --git a/wmake/rules/linux64Gcc/c++ b/wmake/rules/linux64Gcc/c++
index a94b22983a..975c903b03 100644
--- a/wmake/rules/linux64Gcc/c++
+++ b/wmake/rules/linux64Gcc/c++
@@ -1,7 +1,8 @@
 SUFFIXES += .C .cc .cpp .cxx
 
 c++WARN     = -Wall -Wextra -Wold-style-cast -Wnon-virtual-dtor -Wno-unused-parameter \
-              -Wno-invalid-offsetof -Wno-attributes
+              -Wno-invalid-offsetof -Wno-attributes \
+              -Wno-unknown-pragmas
 
 # Suppress some warnings for flex++ and CGAL
 c++LESSWARN = -Wno-old-style-cast -Wno-unused-local-typedefs -Wno-array-bounds
diff --git a/wmake/rules/linuxARM64Gcc/c++ b/wmake/rules/linuxARM64Gcc/c++
index 3985f54a9b..c8bc2d4b5f 100644
--- a/wmake/rules/linuxARM64Gcc/c++
+++ b/wmake/rules/linuxARM64Gcc/c++
@@ -1,7 +1,8 @@
 SUFFIXES += .C .cc .cpp .cxx
 
 c++WARN     = -Wall -Wextra -Wold-style-cast -Wnon-virtual-dtor -Wno-unused-parameter \
-              -Wno-invalid-offsetof -Wno-attributes
+              -Wno-invalid-offsetof -Wno-attributes \
+              -Wno-unknown-pragmas
 
 # Suppress some warnings for flex++ and CGAL
 c++LESSWARN = -Wno-old-style-cast -Wno-unused-local-typedefs -Wno-array-bounds
diff --git a/wmake/rules/linuxARM7Gcc/c++ b/wmake/rules/linuxARM7Gcc/c++
index 3985f54a9b..c8bc2d4b5f 100644
--- a/wmake/rules/linuxARM7Gcc/c++
+++ b/wmake/rules/linuxARM7Gcc/c++
@@ -1,7 +1,8 @@
 SUFFIXES += .C .cc .cpp .cxx
 
 c++WARN     = -Wall -Wextra -Wold-style-cast -Wnon-virtual-dtor -Wno-unused-parameter \
-              -Wno-invalid-offsetof -Wno-attributes
+              -Wno-invalid-offsetof -Wno-attributes \
+              -Wno-unknown-pragmas
 
 # Suppress some warnings for flex++ and CGAL
 c++LESSWARN = -Wno-old-style-cast -Wno-unused-local-typedefs -Wno-array-bounds
diff --git a/wmake/rules/linuxGcc/c++ b/wmake/rules/linuxGcc/c++
index 3076e7e6c0..200a5947df 100644
--- a/wmake/rules/linuxGcc/c++
+++ b/wmake/rules/linuxGcc/c++
@@ -1,7 +1,8 @@
 SUFFIXES += .C .cc .cpp .cxx
 
 c++WARN     = -Wall -Wextra -Wold-style-cast -Wnon-virtual-dtor -Wno-unused-parameter \
-              -Wno-invalid-offsetof -Wno-attributes
+              -Wno-invalid-offsetof -Wno-attributes \
+              -Wno-unknown-pragmas
 
 # Suppress some warnings for flex++ and CGAL
 c++LESSWARN = -Wno-old-style-cast -Wno-unused-local-typedefs -Wno-array-bounds
diff --git a/wmake/rules/linuxIA64Gcc/c++ b/wmake/rules/linuxIA64Gcc/c++
index de9a95ab4b..7085623218 100644
--- a/wmake/rules/linuxIA64Gcc/c++
+++ b/wmake/rules/linuxIA64Gcc/c++
@@ -1,7 +1,8 @@
 SUFFIXES += .C .cc .cpp .cxx
 
 c++WARN     = -Wall -Wextra -Wold-style-cast -Wnon-virtual-dtor -Wno-unused-parameter \
-              -Wno-invalid-offsetof -Wno-attributes
+              -Wno-invalid-offsetof -Wno-attributes \
+              -Wno-unknown-pragmas
 
 # Suppress some warnings for flex++ and CGAL
 c++LESSWARN = -Wno-old-style-cast -Wno-unused-local-typedefs -Wno-array-bounds
diff --git a/wmake/rules/linuxPPC64Gcc/c++ b/wmake/rules/linuxPPC64Gcc/c++
index 1bc42bc7cf..976d7980b3 100644
--- a/wmake/rules/linuxPPC64Gcc/c++
+++ b/wmake/rules/linuxPPC64Gcc/c++
@@ -1,7 +1,8 @@
 SUFFIXES += .C .cc .cpp .cxx
 
 c++WARN     = -Wall -Wextra -Wold-style-cast -Wnon-virtual-dtor -Wno-unused-parameter \
-              -Wno-invalid-offsetof -Wno-attributes
+              -Wno-invalid-offsetof -Wno-attributes \
+              -Wno-unknown-pragmas
 
 # Suppress some warnings for flex++ and CGAL
 c++LESSWARN = -Wno-old-style-cast -Wno-unused-local-typedefs -Wno-array-bounds
diff --git a/wmake/rules/linuxPPC64leGcc/c++ b/wmake/rules/linuxPPC64leGcc/c++
index 341a2b5955..9d21178e15 100644
--- a/wmake/rules/linuxPPC64leGcc/c++
+++ b/wmake/rules/linuxPPC64leGcc/c++
@@ -1,7 +1,8 @@
 SUFFIXES += .C .cc .cpp .cxx
 
 c++WARN     = -Wall -Wextra -Wold-style-cast -Wnon-virtual-dtor -Wno-unused-parameter \
-              -Wno-invalid-offsetof -Wno-attributes
+              -Wno-invalid-offsetof -Wno-attributes \
+              -Wno-unknown-pragmas
 
 # Suppress some warnings for flex++ and CGAL
 c++LESSWARN = -Wno-old-style-cast -Wno-unused-local-typedefs -Wno-array-bounds
diff --git a/wmake/rules/solaris64Gcc/c++ b/wmake/rules/solaris64Gcc/c++
index 74b72eecd8..6bb91e3386 100644
--- a/wmake/rules/solaris64Gcc/c++
+++ b/wmake/rules/solaris64Gcc/c++
@@ -1,7 +1,8 @@
 SUFFIXES += .C .cc .cpp .cxx
 
 c++WARN     = -Wall -Wextra -Wold-style-cast -Wnon-virtual-dtor -Wno-unused-parameter \
-              -Wno-invalid-offsetof -Wno-attributes
+              -Wno-invalid-offsetof -Wno-attributes \
+              -Wno-unknown-pragmas
 
 # Suppress some warnings for flex++ and CGAL
 c++LESSWARN =
diff --git a/wmake/rules/solarisGcc/c++ b/wmake/rules/solarisGcc/c++
index cf37d4c57b..4eb9ee2532 100644
--- a/wmake/rules/solarisGcc/c++
+++ b/wmake/rules/solarisGcc/c++
@@ -1,7 +1,8 @@
 SUFFIXES += .C .cc .cpp .cxx
 
 c++WARN     = -Wall -Wextra -Wold-style-cast -Wnon-virtual-dtor -Wno-unused-parameter \
-              -Wno-invalid-offsetof -Wno-attributes
+              -Wno-invalid-offsetof -Wno-attributes \
+              -Wno-unknown-pragmas
 
 # Suppress some warnings for flex++ and CGAL
 c++LESSWARN =