diff --git a/Makefile b/Makefile
index ec6a1ce..7b9ca81 100644
--- a/Makefile
+++ b/Makefile
@@ -5,8 +5,9 @@
 
 
 TZPFMS_VERSION ?= "$(patsubst v%,%,$(shell git describe))"
-SOURCE_DATE_EPOCH ?= $(shell git log -1 --no-show-signature --format=%at man/klapki.8)
-TZPFMS_DATE ?= $(shell LC_ALL=C date -d@$(SOURCE_DATE_EPOCH) '+%B %e, %Y')
+SOURCE_DATE_EPOCH ?=
+TZPFMS_DATE ?=
+
 
 AWK ?= awk
 SED ?= sed
@@ -19,6 +20,13 @@ OUTDIR := out/
 BLDDIR := out/build/
 
 SYSTEMD_SYSTEM_UNITDIR := $(shell $(PKGCONF) --variable=systemd_system_unit_dir systemd 2>/dev/null || echo /usr/lib/systemd/system)
+ifneq "$(TZPFMS_DATE)" ""
+MANUAL_DATE := $(TZPFMS_DATE)
+else ifneq "$(SOURCE_DATE_EPOCH)" ""
+MANUAL_DATE := $(shell LC_ALL=C date -d@$(SOURCE_DATE_EPOCH) '+%B %e, %Y')
+else
+MANUAL_DATE  = $(shell LC_ALL=C date -d@$(shell git log -1 --no-show-signature --format=%at $(1)) '+%B %e, %Y')
+endif
 
 
 PKGS := libzfs libzfs_core tss2-esys tss2-rc
@@ -111,7 +119,7 @@ $(OUTDIR)systemd/usr/libexec/tzpfms-zfs-load-key@ : init.d/systemd/libexec-tzpfm
 # Can't put it at the very top, since man(1) only loads mdoc *after* the first mdoc macro (.Dd in our case)
 $(OUTDIR)man/% : man/%.pp $(MANPAGE_HEADERS)
 	@mkdir -p $(dir $@)
-	$(AWK) -f pp.awk $< TZPFMS_PASSPHRASE_HELPER_MAN='$(DEF_TPH_MAN)' | $(AWK) '/^$$/ {prev_empty=1; next} $$1 == "#" && $$2 ~ /^[0-9]*$$/ {prev_empty=0; next}  {if(prev_empty) print ""; prev_empty=0; print}' | $(AWK) '$$0 == ".Dd" {$$2 = "$(TZPFMS_DATE)"}  $$1 == ".Dt" { print ".ds doc-volume-operating-system" }  $$0 == ".Os" {$$2 = "tzpfms"; $$3 = $(TZPFMS_VERSION)}  {print}' > $@
+	$(AWK) -f pp.awk $< TZPFMS_PASSPHRASE_HELPER_MAN='$(DEF_TPH_MAN)' | $(AWK) '/^$$/ {prev_empty=1; next} $$1 == "#" && $$2 ~ /^[0-9]*$$/ {prev_empty=0; next}  {if(prev_empty) print ""; prev_empty=0; print}' | $(AWK) '$$0 == ".Dd" {$$2 = "$(call MANUAL_DATE,$<)"}  $$1 == ".Dt" { print ".ds doc-volume-operating-system" }  $$0 == ".Os" {$$2 = "tzpfms"; $$3 = $(TZPFMS_VERSION)}  {print}' > $@
 	! $(MANDOC) -Tlint $@ 2>&1 | grep -vE -e 'mandoc: outdated mandoc.db' -e 'STYLE: referenced manual not found' -e 'STYLE: operating system explicitly specified: Os tzpfms' -e 'WARNING: cross reference to self: Xr zfs-tpm.*-change-key 8' -e 'STYLE: input text line longer than 80 bytes'
 # The "WARNING: unknown font, skipping request: TS.+fC[RBI]" one: see https://bugs.debian.org/992002