diff --git a/config/llvm.m4 b/config/llvm.m4
index 5d4f14cb900..496fd8f72a4 100644
--- a/config/llvm.m4
+++ b/config/llvm.m4
@@ -46,10 +46,13 @@ AC_DEFUN([PGAC_LLVM_SUPPORT],
   # clear what the minimum version is.
 
   # Collect compiler flags necessary to build the LLVM dependent
-  # shared library.
+  # shared library.  The include directories are added with -isystem
+  # rather than -I, so that warnings from LLVM's own headers are not
+  # reported under the warning options we select for our own code.
   for pgac_option in `$LLVM_CONFIG --cppflags`; do
     case $pgac_option in
-      -I*|-D*) LLVM_CPPFLAGS="$pgac_option $LLVM_CPPFLAGS";;
+      -I*) LLVM_CPPFLAGS="-isystem ${pgac_option#-I} $LLVM_CPPFLAGS";;
+      -D*) LLVM_CPPFLAGS="$pgac_option $LLVM_CPPFLAGS";;
     esac
   done
 
diff --git a/configure b/configure
index d42a7a794ff..002e31bf695 100755
--- a/configure
+++ b/configure
@@ -5105,10 +5105,13 @@ fi
   # clear what the minimum version is.
 
   # Collect compiler flags necessary to build the LLVM dependent
-  # shared library.
+  # shared library.  The include directories are added with -isystem
+  # rather than -I, so that warnings from LLVM's own headers are not
+  # reported under the warning options we select for our own code.
   for pgac_option in `$LLVM_CONFIG --cppflags`; do
     case $pgac_option in
-      -I*|-D*) LLVM_CPPFLAGS="$pgac_option $LLVM_CPPFLAGS";;
+      -I*) LLVM_CPPFLAGS="-isystem ${pgac_option#-I} $LLVM_CPPFLAGS";;
+      -D*) LLVM_CPPFLAGS="$pgac_option $LLVM_CPPFLAGS";;
     esac
   done
 
diff --git a/meson.build b/meson.build
index f4cde249242..52d6bc37dd9 100644
--- a/meson.build
+++ b/meson.build
@@ -924,7 +924,10 @@ endif
 llvmopt = get_option('llvm')
 llvm = not_found_dep
 if have_cxx
-  llvm = dependency('llvm', version: '>=14', method: 'config-tool', required: llvmopt)
+  # Use include_type 'system' so that warnings from LLVM's own headers are
+  # not reported under the warning options we select for our own code.
+  llvm = dependency('llvm', version: '>=14', method: 'config-tool',
+                    include_type: 'system', required: llvmopt)
 
   if llvm.found()