Index: share/mk/bsd.links.mk
===================================================================
--- share/mk/bsd.links.mk
+++ share/mk/bsd.links.mk
@@ -15,7 +15,16 @@
 .ORDER: realinstall _installlinks
 _installlinks:
 .for s t in ${LINKS}
+	# Don't delete the source file on a case-insensitive file-system and pass -S
+	# to install to avoid overwriting the source
+.if ${s:tl} == ${t:tl}
+	if test "${DESTDIR}${t}" -ef "${DESTDIR}${s}"; then \
+		echo "Note: installing link from ${l} to ${t} on case-insensitive file system."; \
+	fi
+	${INSTALL_LINK} -S ${TAG_ARGS} ${DESTDIR}${s} ${DESTDIR}${t}
+.else
 	${INSTALL_LINK} ${TAG_ARGS} ${DESTDIR}${s} ${DESTDIR}${t}
+.endif
 .endfor
 .for s t in ${SYMLINKS}
 	${INSTALL_SYMLINK} ${TAG_ARGS} ${s} ${DESTDIR}${t}
Index: share/mk/bsd.man.mk
===================================================================
--- share/mk/bsd.man.mk
+++ share/mk/bsd.man.mk
@@ -226,8 +226,19 @@
 .endif	# ${MK_MANCOMPRESS} == "no"
 .endif
 .for l t in ${_MANLINKS}
+.if ${l:tl} == ${t:tl}
+	# Don't delete the source file on a case-insensitive file-system and pass -S
+	# to install to avoid overwriting the source
+	if test "${DESTDIR}${l}${ZEXT}" -ef "${DESTDIR}${t}${ZEXT}"; then \
+		echo "Note: installing man link from ${l} to ${t} on case-insensitive file system."; \
+	else \
+		rm -f ${DESTDIR}${t} ${DESTDIR}${t}${MCOMPRESS_EXT}; \
+	fi
+	${INSTALL_MANLINK} -S ${TAG_ARGS} ${DESTDIR}${l}${ZEXT} ${DESTDIR}${t}${ZEXT}
+.else
 	rm -f ${DESTDIR}${t} ${DESTDIR}${t}${MCOMPRESS_EXT}; \
 	    ${INSTALL_MANLINK} ${TAG_ARGS} ${DESTDIR}${l}${ZEXT} ${DESTDIR}${t}${ZEXT}
+.endif
 .endfor
 
 manlint:
Index: tools/install.sh
===================================================================
--- tools/install.sh
+++ tools/install.sh
@@ -62,6 +62,14 @@
 
 # the remaining arguments are assumed to be files/dirs only.
 if [ -n "${linkmode}" ]; then
+	# Don't delete the source file on a case insensitive file system since
+	# `ln -f` will remove the file first and then attempt to create the link
+	src_lower=$(echo "$1" | awk '{print tolower($0)}')
+	target_lower=$(echo "$2" | awk '{print tolower($0)}')
+	if [ "$src_lower" = "$target_lower" ] && test "$1" -ef "$2"; then
+		echo "$0: not creating link from $1 to $2 on case-insensitive file system." >&2
+		exit 0
+	fi
 	if [ "${linkmode}" = "symbolic" ]; then
 		ln -fsn "$@"
 	else