diff --git a/Documentation/git-fmt-merge-msg.txt b/Documentation/git-fmt-merge-msg.txt
index f04a9ff0e0299bdb6f33d10f5674cc19dc2777f7..40dba8c0a9f308064f67d8f38ce8a22b2a42a77c 100644
--- a/Documentation/git-fmt-merge-msg.txt
+++ b/Documentation/git-fmt-merge-msg.txt
@@ -54,8 +54,10 @@ CONFIGURATION
 -------------
 
 merge.log::
-	Whether to include summaries of merged commits in newly
-	merge commit messages. False by default.
+	In addition to branch names, populate the log message with at
+	most the specified number of one-line descriptions from the
+	actual commits that are being merged.  Defaults to false, and
+	true is a synoym for 20.
 
 merge.summary::
 	Synonym to `merge.log`; this is deprecated and will be removed in
diff --git a/Documentation/merge-config.txt b/Documentation/merge-config.txt
index a403155052299dd0aaafd6bdfe0fec92d0d0ac7c..acbe1e16b2c6b3ea5f7cfe20a9a3794c6e982ac8 100644
--- a/Documentation/merge-config.txt
+++ b/Documentation/merge-config.txt
@@ -7,8 +7,10 @@ merge.conflictstyle::
 	marker and the original text before the `=======` marker.
 
 merge.log::
-	Whether to include summaries of merged commits in newly created
-	merge commit messages. False by default.
+	In addition to branch names, populate the log message with at
+	most the specified number of one-line descriptions from the
+	actual commits that are being merged.  Defaults to false, and
+	true is a synoym for 20.
 
 merge.renameLimit::
 	The number of files to consider when performing rename detection
diff --git a/builtin/fmt-merge-msg.c b/builtin/fmt-merge-msg.c
index 455e7c67f885e7a8584066fca6f759ddd27443db..d2eed43ab5c165f3b0ed10ba3df4296fc4679dd2 100644
--- a/builtin/fmt-merge-msg.c
+++ b/builtin/fmt-merge-msg.c
@@ -15,15 +15,13 @@ static int shortlog_len;
 
 static int fmt_merge_msg_config(const char *key, const char *value, void *cb)
 {
-	static int found_merge_log = 0;
-	if (!strcmp("merge.log", key)) {
-		found_merge_log = 1;
-		shortlog_len = git_config_bool(key, value) ? DEFAULT_MERGE_LOG_LEN : 0;
-		return 0;
-	}
-	if (!found_merge_log && !strcmp("merge.summary", key)) {
-		shortlog_len = git_config_bool(key, value) ? DEFAULT_MERGE_LOG_LEN : 0;
-		return 0;
+	if (!strcmp(key, "merge.log") || !strcmp(key, "merge.summary")) {
+		int is_bool;
+		shortlog_len = git_config_bool_or_int(key, value, &is_bool);
+		if (!is_bool && shortlog_len < 0)
+			return error("%s: negative length %s", key, value);
+		if (is_bool && shortlog_len)
+			shortlog_len = DEFAULT_MERGE_LOG_LEN;
 	}
 	return 0;
 }
diff --git a/builtin/merge.c b/builtin/merge.c
index 9e4733d25f94a4185acb99cbc53255cee2654c1b..1e9c898aec2834577689b430739607a50508498a 100644
--- a/builtin/merge.c
+++ b/builtin/merge.c
@@ -503,7 +503,12 @@ static int git_merge_config(const char *k, const char *v, void *cb)
 	else if (!strcmp(k, "pull.octopus"))
 		return git_config_string(&pull_octopus, k, v);
 	else if (!strcmp(k, "merge.log") || !strcmp(k, "merge.summary")) {
-		shortlog_len = git_config_bool(k, v) ? DEFAULT_MERGE_LOG_LEN : 0;
+		int is_bool;
+		shortlog_len = git_config_bool_or_int(k, v, &is_bool);
+		if (!is_bool && shortlog_len < 0)
+			return error("%s: negative length %s", k, v);
+		if (is_bool && shortlog_len)
+			shortlog_len = DEFAULT_MERGE_LOG_LEN;
 		return 0;
 	}
 	return git_diff_ui_config(k, v, cb);