Index: /issm/trunk-jpl/externalpackages/petsc/install-3.12-mac-static.sh
===================================================================
--- /issm/trunk-jpl/externalpackages/petsc/install-3.12-mac-static.sh	(revision 25799)
+++ /issm/trunk-jpl/externalpackages/petsc/install-3.12-mac-static.sh	(revision 25800)
@@ -29,6 +29,7 @@
 #		Either run using --with-shared-libraries or --with-pic=0 and supply the
 #		compiler PIC flag via CFLAGS, CXXXFLAGS, and FCFLAGS
+#
 # - Added -Wno-error=implicit-function-declaration to CFLAGS for Clang >= 12. 
-#	May need to remove it for earlier versions not using the C99 standard.
+#	(may need to remove it for earlier versions not using the C99 standard).
 # - Added -fallow-argument-mismatch to FFLAGS in order to clear,
 #
@@ -36,6 +37,5 @@
 #		the same routine with arguments of different types.
 #
-#	This has only been added to macOS static builds, but may be needed 
-#	elsewhere.
+#	for gfortran 10 or later (may need to remove it for earlier versions).
 # - Added -static-libgfortran to all macOS static builds, but this will not 
 #	work out of the box on Linux.
Index: /issm/trunk-jpl/externalpackages/petsc/install-3.12-mac.sh
===================================================================
--- /issm/trunk-jpl/externalpackages/petsc/install-3.12-mac.sh	(revision 25799)
+++ /issm/trunk-jpl/externalpackages/petsc/install-3.12-mac.sh	(revision 25800)
@@ -29,5 +29,7 @@
 #		the same routine with arguments of different types.
 #
-#	for gfortran 10 or later.
+#	for gfortran 10 or later (may need to remove it for earlier versions).
+# - Added -Wno-error=implicit-function-declaration to CFLAGS for Clang >= 12. 
+#	(may need to remove it for earlier versions not using the C99 standard).
 #
 cd src
@@ -35,4 +37,5 @@
 	--prefix="${ISSM_DIR}/externalpackages/petsc/install" \
 	--PETSC_DIR="${ISSM_DIR}/externalpackages/petsc/src" \
+	--CFLAGS="-Wno-error=implicit-function-declaration" \
 	--FFLAGS="-fallow-argument-mismatch" \
 	--with-debugging=0 \
Index: /issm/trunk-jpl/externalpackages/petsc/install-3.14-mac.sh
===================================================================
--- /issm/trunk-jpl/externalpackages/petsc/install-3.14-mac.sh	(revision 25799)
+++ /issm/trunk-jpl/externalpackages/petsc/install-3.14-mac.sh	(revision 25800)
@@ -21,8 +21,21 @@
 
 # Configure
+#
+# NOTE:
+# - 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).
+# - Added -Wno-error=implicit-function-declaration to CFLAGS for Clang >= 12. 
+#	(may need to remove it for earlier versions not using the C99 standard).
+#
 cd src
 ./config/configure.py \
 	--prefix="${ISSM_DIR}/externalpackages/petsc/install" \
 	--PETSC_DIR="${ISSM_DIR}/externalpackages/petsc/src" \
+	--CFLAGS="-Wno-error=implicit-function-declaration" \
+	--FFLAGS="-fallow-argument-mismatch" \
 	--with-debugging=0 \
 	--with-valgrind=0 \