diff --git a/gitk-git/gitk b/gitk-git/gitk
index 23d9dd1fe0d0..2da53604cdc8 100755
--- a/gitk-git/gitk
+++ b/gitk-git/gitk
@@ -290,6 +290,7 @@ proc parseviewargs {n arglist} {
 
 proc parseviewrevs {view revs} {
     global vposids vnegids
+    global hashlength
 
     if {$revs eq {}} {
         set revs HEAD
@@ -303,7 +304,7 @@ proc parseviewrevs {view revs} {
         set badrev {}
         for {set l 0} {$l < [llength $errlines]} {incr l} {
             set line [lindex $errlines $l]
-            if {!([string length $line] == 40 && [string is xdigit $line])} {
+            if {!([string length $line] == $hashlength && [string is xdigit $line])} {
                 if {[string match "fatal:*" $line]} {
                     if {[string match "fatal: ambiguous argument*" $line]
                         && $badrev ne {}} {
@@ -507,6 +508,7 @@ proc updatecommits {} {
     global hasworktree
     global varcid vposids vnegids vflags vrevs
     global show_notes
+    global hashlength
 
     set hasworktree [hasworktree]
     rereadrefs
@@ -540,7 +542,7 @@ proc updatecommits {} {
             # take out positive refs that we asked for before or
             # that we have already seen
             foreach rev $revs {
-                if {[string length $rev] == 40} {
+                if {[string length $rev] == $hashlength} {
                     if {[lsearch -exact $oldpos $rev] < 0
                         && ![info exists varcid($view,$rev)]} {
                         lappend newrevs $rev
@@ -1418,6 +1420,7 @@ proc getcommitlines {fd inst view updating}  {
     global parents children curview hlview
     global idpending ordertok
     global varccommits varcid varctok vtokmod vfilelimit vshortids
+    global hashlength
 
     set stuff [read $fd 500000]
     # git log doesn't terminate the last commit with a null...
@@ -1500,7 +1503,7 @@ proc getcommitlines {fd inst view updating}  {
             }
             set ok 1
             foreach id $ids {
-                if {[string length $id] != 40} {
+                if {[string length $id] != $hashlength} {
                     set ok 0
                     break
                 }
@@ -1780,6 +1783,7 @@ proc readrefs {} {
     global selecthead selectheadid
     global hideremotes
     global tclencoding
+    global hashlength
 
     foreach v {tagids idtags headids idheads otherrefids idotherrefs} {
         unset -nocomplain $v
@@ -1789,9 +1793,9 @@ proc readrefs {} {
         fconfigure $refd -encoding $tclencoding
     }
     while {[gets $refd line] >= 0} {
-        if {[string index $line 40] ne " "} continue
-        set id [string range $line 0 39]
-        set ref [string range $line 41 end]
+        if {[string index $line $hashlength] ne " "} continue
+        set id [string range $line 0 [expr {$hashlength - 1}]]
+        set ref [string range $line [expr {$hashlength + 1}] end]
         if {![string match "refs/*" $ref]} continue
         set name [string range $ref 5 end]
         if {[string match "remotes/*" $name]} {
@@ -2082,6 +2086,7 @@ proc makewindow {} {
     global have_tk85 use_ttk NS
     global git_version
     global worddiff
+    global hashlength hashalgorithm
 
     # The "mc" arguments here are purely so that xgettext
     # sees the following string as needing to be translated
@@ -2203,11 +2208,11 @@ proc makewindow {} {
     set sha1entry .tf.bar.sha1
     set entries $sha1entry
     set sha1but .tf.bar.sha1label
-    button $sha1but -text "[mc "SHA1 ID:"] " -state disabled -relief flat \
+    button $sha1but -text "[mc "$hashalgorithm ID:"] " -state disabled -relief flat \
         -command gotocommit -width 8
     $sha1but conf -disabledforeground [$sha1but cget -foreground]
     pack .tf.bar.sha1label -side left
-    ${NS}::entry $sha1entry -width 40 -font textfont -textvariable sha1string
+    ${NS}::entry $sha1entry -width $hashlength -font textfont -textvariable sha1string
     trace add variable sha1string write sha1change
     pack $sha1entry -side left -pady 2
 
@@ -3926,6 +3931,7 @@ proc stopblaming {} {
 
 proc read_line_source {fd inst} {
     global blamestuff curview commfd blameinst nullid nullid2
+    global hashlength
 
     while {[gets $fd line] >= 0} {
         lappend blamestuff($inst) $line
@@ -3946,7 +3952,7 @@ proc read_line_source {fd inst} {
     set line [split [lindex $blamestuff($inst) 0] " "]
     set id [lindex $line 0]
     set lnum [lindex $line 1]
-    if {[string length $id] == 40 && [string is xdigit $id] &&
+    if {[string length $id] == $hashlength && [string is xdigit $id] &&
         [string is digit -strict $lnum]} {
         # look for "filename" line
         foreach l $blamestuff($inst) {
@@ -5269,13 +5275,14 @@ proc get_viewmainhead {view} {
 # git rev-list should give us just 1 line to use as viewmainheadid($view)
 proc getviewhead {fd inst view} {
     global viewmainheadid commfd curview viewinstances showlocalchanges
+    global hashlength
 
     set id {}
     if {[gets $fd line] < 0} {
         if {![eof $fd]} {
             return 1
         }
-    } elseif {[string length $line] == 40 && [string is xdigit $line]} {
+    } elseif {[string length $line] == $hashlength && [string is xdigit $line]} {
         set id $line
     }
     set viewmainheadid($view) $id
@@ -7039,10 +7046,11 @@ proc commit_descriptor {p} {
 # Also look for URLs of the form "http[s]://..." and make them web links.
 proc appendwithlinks {text tags} {
     global ctext linknum curview
+    global hashlength
 
     set start [$ctext index "end - 1c"]
     $ctext insert end $text $tags
-    set links [regexp -indices -all -inline {(?:\m|-g)[0-9a-f]{6,40}\M} $text]
+    set links [regexp -indices -all -inline [string map "@@ $hashlength" {(?:\m|-g)[0-9a-f]{6,@@}\M}] $text]
     foreach l $links {
         set s [lindex $l 0]
         set e [lindex $l 1]
@@ -8716,13 +8724,17 @@ proc incrfont {inc} {
 
 proc clearsha1 {} {
     global sha1entry sha1string
-    if {[string length $sha1string] == 40} {
+    global hashlength
+
+    if {[string length $sha1string] == $hashlength} {
         $sha1entry delete 0 end
     }
 }
 
 proc sha1change {n1 n2 op} {
     global sha1string currentid sha1but
+    global hashalgorithm
+
     if {$sha1string == {}
         || ([info exists currentid] && $sha1string == $currentid)} {
         set state disabled
@@ -8733,12 +8745,13 @@ proc sha1change {n1 n2 op} {
     if {$state == "normal"} {
         $sha1but conf -state normal -relief raised -text "[mc "Goto:"] "
     } else {
-        $sha1but conf -state disabled -relief flat -text "[mc "SHA1 ID:"] "
+        $sha1but conf -state disabled -relief flat -text "[mc "$hashalgorithm ID:"] "
     }
 }
 
 proc gotocommit {} {
     global sha1string tagids headids curview varcid
+    global hashlength hashalgorithm
 
     if {$sha1string == {}
         || ([info exists currentid] && $sha1string == $currentid)} return
@@ -8748,11 +8761,11 @@ proc gotocommit {} {
         set id $headids($sha1string)
     } else {
         set id [string tolower $sha1string]
-        if {[regexp {^[0-9a-f]{4,39}$} $id]} {
+        if {[regexp [string map "@@ [expr $hashlength - 1]" {^[0-9a-f]{4,@@}$}] $id]} {
             set matches [longid $id]
             if {$matches ne {}} {
                 if {[llength $matches] > 1} {
-                    error_popup [mc "Short SHA1 id %s is ambiguous" $id]
+                    error_popup [mc "Short $hashalgorithm id %s is ambiguous" $id]
                     return
                 }
                 set id [lindex $matches 0]
@@ -8769,7 +8782,7 @@ proc gotocommit {} {
         return
     }
     if {[regexp {^[0-9a-fA-F]{4,}$} $sha1string]} {
-        set msg [mc "SHA1 id %s is not known" $sha1string]
+        set msg [mc "$hashalgorithm id %s is not known" $sha1string]
     } else {
         set msg [mc "Revision %s is not in the current view" $sha1string]
     }
@@ -9446,10 +9459,11 @@ proc mktaggo {} {
 
 proc copyreference {} {
     global rowmenuid autosellen
+    global hashlength
 
     set format "%h (\"%s\", %ad)"
     set cmd [list git show -s --pretty=format:$format --date=short]
-    if {$autosellen < 40} {
+    if {$autosellen < $hashlength} {
         lappend cmd --abbrev=$autosellen
     }
     set reference [eval exec $cmd $rowmenuid]
@@ -9460,6 +9474,7 @@ proc copyreference {} {
 
 proc writecommit {} {
     global rowmenuid wrcomtop commitinfo wrcomcmd NS
+    global hashlength
 
     set top .writecommit
     set wrcomtop $top
@@ -9469,7 +9484,7 @@ proc writecommit {} {
     ${NS}::label $top.title -text [mc "Write commit to file"]
     grid $top.title - -pady 10
     ${NS}::label $top.id -text [mc "ID:"]
-    ${NS}::entry $top.sha1 -width 40
+    ${NS}::entry $top.sha1 -width $hashlength
     $top.sha1 insert 0 $rowmenuid
     $top.sha1 conf -state readonly
     grid $top.id $top.sha1 -sticky w
@@ -9549,6 +9564,7 @@ proc mvbranch {} {
 
 proc branchdia {top valvar uivar} {
     global NS commitinfo
+    global hashlength
     upvar $valvar val $uivar ui
 
     catch {destroy $top}
@@ -9557,7 +9573,7 @@ proc branchdia {top valvar uivar} {
     ${NS}::label $top.title -text $ui(title)
     grid $top.title - -pady 10
     ${NS}::label $top.id -text [mc "ID:"]
-    ${NS}::entry $top.sha1 -width 40
+    ${NS}::entry $top.sha1 -width $hashlength
     $top.sha1 insert 0 $val(id)
     $top.sha1 conf -state readonly
     grid $top.id $top.sha1 -sticky w
@@ -12320,6 +12336,18 @@ if {$tclencoding == {}} {
     puts stderr "Warning: encoding $gitencoding is not supported by Tcl/Tk"
 }
 
+set objformat [exec git rev-parse --show-object-format]
+if {$objformat eq "sha1"} {
+    set hashlength 40
+} elseif {$objformat eq "sha256"} {
+    set hashlength 64
+} else {
+    error_popup "[mc "Not supported hash algorithm:"] {$objformat}"
+    exit 1
+}
+set hashalgorithm [string toupper $objformat]
+unset objformat
+
 set gui_encoding [encoding system]
 catch {
     set enc [exec git config --get gui.encoding]
