diff --git a/git-gui.sh b/git-gui.sh
index dba585111c..d6472636c3 100755
--- a/git-gui.sh
+++ b/git-gui.sh
@@ -2038,17 +2038,17 @@ lappend diff_actions [list $ctxm entryconf [$ctxm index last] -state]
 $ctxm add separator
 $ctxm add command \
 	-label {Show Less Context} \
-	-command {if {$repo_config(gui.diffcontext) >= 2} {
+	-command {if {$repo_config(gui.diffcontext) >= 1} {
 		incr repo_config(gui.diffcontext) -1
 		reshow_diff
 	}}
 lappend diff_actions [list $ctxm entryconf [$ctxm index last] -state]
 $ctxm add command \
 	-label {Show More Context} \
-	-command {
+	-command {if {$repo_config(gui.diffcontext) < 99} {
 		incr repo_config(gui.diffcontext)
 		reshow_diff
-	}
+	}}
 lappend diff_actions [list $ctxm entryconf [$ctxm index last] -state]
 $ctxm add separator
 $ctxm add command -label {Options...} \
diff --git a/lib/diff.tcl b/lib/diff.tcl
index 7e715a6865..29436b50cb 100644
--- a/lib/diff.tcl
+++ b/lib/diff.tcl
@@ -145,7 +145,7 @@ proc show_diff {path w {lno {}}} {
 
 	lappend cmd -p
 	lappend cmd --no-color
-	if {$repo_config(gui.diffcontext) > 0} {
+	if {$repo_config(gui.diffcontext) >= 0} {
 		lappend cmd "-U$repo_config(gui.diffcontext)"
 	}
 	if {$w eq $ui_index} {
diff --git a/lib/option.tcl b/lib/option.tcl
index 17fcc65f78..11dd9be6b9 100644
--- a/lib/option.tcl
+++ b/lib/option.tcl
@@ -173,7 +173,7 @@ proc do_options {} {
 		{i-1..5 merge.verbosity {Merge Verbosity}}
 
 		{b gui.trustmtime  {Trust File Modification Timestamps}}
-		{i-1..99 gui.diffcontext {Number of Diff Context Lines}}
+		{i-0..99 gui.diffcontext {Number of Diff Context Lines}}
 		{t gui.newbranchtemplate {New Branch Name Template}}
 		} {
 		set type [lindex $option 0]