Index: /issm/trunk-jpl/externalpackages/petsc/install-3.16-linux.sh
===================================================================
--- /issm/trunk-jpl/externalpackages/petsc/install-3.16-linux.sh	(revision 27324)
+++ /issm/trunk-jpl/externalpackages/petsc/install-3.16-linux.sh	(revision 27325)
@@ -2,7 +2,8 @@
 set -eu
 
+
 ## Constants
 #
-VER="3.16.0"
+VER="3.16.6"
 
 PETSC_DIR="${ISSM_DIR}/externalpackages/petsc/src" # DO NOT CHANGE THIS
@@ -24,9 +25,21 @@
 
 # Configure
+#
+# NOTE:
+# - Added -Wno-error=implicit-function-declaration to CFLAGS for Clang >= 12. 
+#	(may need to remove it for earlier versions not using the C99 standard).
+# - Added -fallow-argument-mismatch to FFLAGS in order to clear,
+#
+#		error: The Fortran compiler gfortran will not compile files that call 
+#		the same routine with arguments of different types.
+#
+#	for gfortran 10 or later (may need to remove it for earlier versions).
+#
 cd ${PETSC_DIR}
 ./configure \
 	--prefix="${PREFIX}" \
 	--PETSC_DIR="${PETSC_DIR}" \
-	-COPTFLAGS="-g -O2" -CXXOPTFLAGS="-g -O2" -FOPTFLAGS="-g -O2" \
+	--CFLAGS="-Wno-error=implicit-function-declaration" \
+	--FFLAGS="-fallow-argument-mismatch" \
 	--with-debugging=0 \
 	--with-valgrind=0 \
Index: /issm/trunk-jpl/externalpackages/petsc/install-3.16-pleiades.sh
===================================================================
--- /issm/trunk-jpl/externalpackages/petsc/install-3.16-pleiades.sh	(revision 27324)
+++ /issm/trunk-jpl/externalpackages/petsc/install-3.16-pleiades.sh	(revision 27325)
@@ -5,5 +5,5 @@
 ## Constants
 #
-VER="3.16.4"
+VER="3.16.6"
 
 PETSC_DIR="${ISSM_DIR}/externalpackages/petsc/src" # DO NOT CHANGE THIS