diff --git a/gf180mcu/Makefile.in b/gf180mcu/Makefile.in
index 289e5b7..11856c2 100644
--- a/gf180mcu/Makefile.in
+++ b/gf180mcu/Makefile.in
@@ -485,6 +485,13 @@
         TOOLS += xcircuit
 endif
 
+# This definition depends on the setting of EF_STYLE
+ifeq (${EF_STYLE}, 1)
+	IO_GDS = gds/gf180mcu_fd_io
+else
+	IO_GDS = gf180mcu_fd_io/gds
+endif
+
 all: $(foreach var, ${VARIANTS}, all-$(var))
 
 reference: ${TECH}.json
@@ -1182,6 +1189,10 @@
 	# in the corner clamp cell that contains the devices being isolated.
 	${ADDLAYER} ${STAGING_PATH}/${GF180MCU$*} gf180mcu_fd_io ESD_CLAMP_COR \
 		isosubstrate "-42 43458 56113 57130 40932 43016 57057 55812" -mag
+	# Permanent solution to the extraction issue---modify the GDS with the
+	# isolated substrate layer.
+	./custom/scripts/fix_io_cor_gds.py \
+		${STAGING_PATH}/${GF180MCU$*}/libs.ref/${IO_GDS}/gf180mcu_fd_io.gds
 
 sram-%:
 	# Install SRAM macros from vendor files
diff --git a/gf180mcu/custom/scripts/fix_io_cor_gds.py b/gf180mcu/custom/scripts/fix_io_cor_gds.py
new file mode 100755
index 0000000..397a7d3
--- /dev/null
+++ b/gf180mcu/custom/scripts/fix_io_cor_gds.py
@@ -0,0 +1,42 @@
+#!/usr/bin/env python3
+#
+# fix_io_cor_gds.py ---
+#
+# Special-purpose script that does the work of what ought to be a simple
+# binary diff and patch.  Except that no such thing exists as a standard
+# offering on most Linux systems, so instead of adding another OS
+# package requirement, I'm just writing a binary search-and-replace in
+# python.
+#
+# The purpose of the patch is to add the isolated substrate layer
+# (GDS layer 23:5) to the ESD_CLAMP_COR cell, which is the only way to
+# get the cell to be LVS-correct at that level of hierarchy.  The layer
+# is simply copied down from further up in the hierarchy.  There is no
+# mask change to the corner cell itself, but the change allows the corner
+# cell to be read back from GDS, extract, and pass LVS.
+
+import sys
+
+if len(sys.argv) != 2:
+    print('Usage:  fix_io_cor_gds.py <filename>')
+    sys.exit(1)
+else:
+    file_name = sys.argv[1]
+
+# orig_data is the STRNAME record for ESD_CLAMP_COR.  Insert the isosub layer
+# data after this record.
+orig_data = b'\x00\x12\x06\x06\x45\x53\x44\x5f\x43\x4c\x41\x4d\x50\x5f\x43\x4f\x52\x00'
+
+append_data = b'\x00\x04\x08\x00\x00\x06\x0d\x02\x00\x17\x00\x06\x0e\x02\x00\x05\x00\x3c\x10\x03\xff\xff\xff\x2e\x00\x03\x48\x2d\xff\xff\xff\x2e\x00\x04\x5b\xd2\x00\x04\x47\xf5\x00\x04\x5b\xd2\x00\x04\x47\xf5\x00\x04\x42\x14\x00\x04\x5a\x65\x00\x04\x42\x14\x00\x04\x5a\x65\x00\x03\x48\x2d\xff\xff\xff\x2e\x00\x03\x48\x2d\x00\x04\x11\x00'
+
+# This is not efficient, but only needs to be done once.
+
+with open(file_name, 'rb') as ifile:
+    data = ifile.read()
+    data = data.replace(orig_data, orig_data + append_data)
+
+# Write back into the same file
+with open(file_name, 'wb') as ofile:
+    ofile.write(data)
+
+print("Done!")