diff --git a/commit.c b/commit.c
index b4512ab0b2..66a3f4e8f4 100644
--- a/commit.c
+++ b/commit.c
@@ -1041,6 +1041,65 @@ static void handle_signed_tag(struct commit *parent, struct commit_extra_header
 	free(buf);
 }
 
+static struct {
+	char result;
+	const char *check;
+} sigcheck_gpg_status[] = {
+	{ 'G', "\n[GNUPG:] GOODSIG " },
+	{ 'B', "\n[GNUPG:] BADSIG " },
+};
+
+static void parse_gpg_output(struct signature_check *sigc)
+{
+	const char *buf = sigc->gpg_status;
+	int i;
+
+	for (i = 0; i < ARRAY_SIZE(sigcheck_gpg_status); i++) {
+		const char *found = strstr(buf, sigcheck_gpg_status[i].check);
+		const char *next;
+		if (!found)
+			continue;
+		sigc->result = sigcheck_gpg_status[i].result;
+		found += strlen(sigcheck_gpg_status[i].check);
+		sigc->key = xmemdupz(found, 16);
+		found += 17;
+		next = strchrnul(found, '\n');
+		sigc->signer = xmemdupz(found, next - found);
+		break;
+	}
+}
+
+void check_commit_signature(const struct commit* commit, struct signature_check *sigc)
+{
+	struct strbuf payload = STRBUF_INIT;
+	struct strbuf signature = STRBUF_INIT;
+	struct strbuf gpg_output = STRBUF_INIT;
+	struct strbuf gpg_status = STRBUF_INIT;
+	int status;
+
+	sigc->result = 'N';
+
+	if (parse_signed_commit(commit->object.sha1,
+				&payload, &signature) <= 0)
+		goto out;
+	status = verify_signed_buffer(payload.buf, payload.len,
+				      signature.buf, signature.len,
+				      &gpg_output, &gpg_status);
+	if (status && !gpg_output.len)
+		goto out;
+	sigc->gpg_output = strbuf_detach(&gpg_output, NULL);
+	sigc->gpg_status = strbuf_detach(&gpg_status, NULL);
+	parse_gpg_output(sigc);
+
+ out:
+	strbuf_release(&gpg_status);
+	strbuf_release(&gpg_output);
+	strbuf_release(&payload);
+	strbuf_release(&signature);
+}
+
+
+
 void append_merge_tag_headers(struct commit_list *parents,
 			      struct commit_extra_header ***tail)
 {
diff --git a/commit.h b/commit.h
index 2d90d9c27c..c24b844ad6 100644
--- a/commit.h
+++ b/commit.h
@@ -5,6 +5,7 @@
 #include "tree.h"
 #include "strbuf.h"
 #include "decorate.h"
+#include "gpg-interface.h"
 
 struct commit_list {
 	struct commit *item;
@@ -232,4 +233,13 @@ extern void print_commit_list(struct commit_list *list,
 			      const char *format_cur,
 			      const char *format_last);
 
+/*
+ * Check the signature of the given commit. The result of the check is stored in
+ * sig->result, 'G' for a good signature, 'B' for a bad signature and 'N'
+ * for no signature at all.
+ * This may allocate memory for sig->gpg_output, sig->gpg_status, sig->signer
+ * and sig->key.
+ */
+extern void check_commit_signature(const struct commit* commit, struct signature_check *sigc);
+
 #endif /* COMMIT_H */
diff --git a/gpg-interface.h b/gpg-interface.h
index cf99021842..5884aa4052 100644
--- a/gpg-interface.h
+++ b/gpg-interface.h
@@ -1,6 +1,17 @@
 #ifndef GPG_INTERFACE_H
 #define GPG_INTERFACE_H
 
+struct signature_check {
+	char *gpg_output;
+	char *gpg_status;
+	char result; /* 0 (not checked),
+		      * N (checked but no further result),
+		      * G (good)
+		      * B (bad) */
+	char *signer;
+	char *key;
+};
+
 extern int sign_buffer(struct strbuf *buffer, struct strbuf *signature, const char *signing_key);
 extern int verify_signed_buffer(const char *payload, size_t payload_size, const char *signature, size_t signature_size, struct strbuf *gpg_output, struct strbuf *gpg_status);
 extern int git_gpg_config(const char *, const char *, void *);
diff --git a/pretty.c b/pretty.c
index 41f04e669d..35b592ad83 100644
--- a/pretty.c
+++ b/pretty.c
@@ -766,14 +766,7 @@ struct format_commit_context {
 	const struct pretty_print_context *pretty_ctx;
 	unsigned commit_header_parsed:1;
 	unsigned commit_message_parsed:1;
-	unsigned commit_signature_parsed:1;
-	struct {
-		char *gpg_output;
-		char *gpg_status;
-		char good_bad;
-		char *signer;
-		char *key;
-	} signature;
+	struct signature_check signature_check;
 	char *message;
 	size_t width, indent1, indent2;
 
@@ -956,64 +949,6 @@ static void rewrap_message_tail(struct strbuf *sb,
 	c->indent2 = new_indent2;
 }
 
-static struct {
-	char result;
-	const char *check;
-} signature_check[] = {
-	{ 'G', "\n[GNUPG:] GOODSIG " },
-	{ 'B', "\n[GNUPG:] BADSIG " },
-};
-
-static void parse_signature_lines(struct format_commit_context *ctx)
-{
-	const char *buf = ctx->signature.gpg_status;
-	int i;
-
-	for (i = 0; i < ARRAY_SIZE(signature_check); i++) {
-		const char *found = strstr(buf, signature_check[i].check);
-		const char *next;
-		if (!found)
-			continue;
-		ctx->signature.good_bad = signature_check[i].result;
-		found += strlen(signature_check[i].check);
-		ctx->signature.key = xmemdupz(found, 16);
-		found += 17;
-		next = strchrnul(found, '\n');
-		ctx->signature.signer = xmemdupz(found, next - found);
-		break;
-	}
-}
-
-static void parse_commit_signature(struct format_commit_context *ctx)
-{
-	struct strbuf payload = STRBUF_INIT;
-	struct strbuf signature = STRBUF_INIT;
-	struct strbuf gpg_output = STRBUF_INIT;
-	struct strbuf gpg_status = STRBUF_INIT;
-	int status;
-
-	ctx->commit_signature_parsed = 1;
-
-	if (parse_signed_commit(ctx->commit->object.sha1,
-				&payload, &signature) <= 0)
-		goto out;
-	status = verify_signed_buffer(payload.buf, payload.len,
-				      signature.buf, signature.len,
-				      &gpg_output, &gpg_status);
-	if (status && !gpg_output.len)
-		goto out;
-	ctx->signature.gpg_output = strbuf_detach(&gpg_output, NULL);
-	ctx->signature.gpg_status = strbuf_detach(&gpg_status, NULL);
-	parse_signature_lines(ctx);
-
- out:
-	strbuf_release(&gpg_status);
-	strbuf_release(&gpg_output);
-	strbuf_release(&payload);
-	strbuf_release(&signature);
-}
-
-
 static int format_reflog_person(struct strbuf *sb,
 				char part,
 				struct reflog_walk_info *log,
@@ -1199,27 +1134,27 @@ static size_t format_commit_one(struct strbuf *sb, const char *placeholder,
 	}
 
 	if (placeholder[0] == 'G') {
-		if (!c->commit_signature_parsed)
-			parse_commit_signature(c);
+		if (!c->signature_check.result)
+			check_commit_signature(c->commit, &(c->signature_check));
 		switch (placeholder[1]) {
 		case 'G':
-			if (c->signature.gpg_output)
-				strbuf_addstr(sb, c->signature.gpg_output);
+			if (c->signature_check.gpg_output)
+				strbuf_addstr(sb, c->signature_check.gpg_output);
 			break;
 		case '?':
-			switch (c->signature.good_bad) {
+			switch (c->signature_check.result) {
 			case 'G':
 			case 'B':
-				strbuf_addch(sb, c->signature.good_bad);
+				strbuf_addch(sb, c->signature_check.result);
 			}
 			break;
 		case 'S':
-			if (c->signature.signer)
-				strbuf_addstr(sb, c->signature.signer);
+			if (c->signature_check.signer)
+				strbuf_addstr(sb, c->signature_check.signer);
 			break;
 		case 'K':
-			if (c->signature.key)
-				strbuf_addstr(sb, c->signature.key);
+			if (c->signature_check.key)
+				strbuf_addstr(sb, c->signature_check.key);
 			break;
 		}
 		return 2;
@@ -1357,8 +1292,8 @@ void format_commit_message(const struct commit *commit,
 	rewrap_message_tail(sb, &context, 0, 0, 0);
 
 	logmsg_free(context.message, commit);
-	free(context.signature.gpg_output);
-	free(context.signature.signer);
+	free(context.signature_check.gpg_output);
+	free(context.signature_check.signer);
 }
 
 static void pp_header(const struct pretty_print_context *pp,