--- test019.left.txt
+++ test019.right.txt
@@ -40,8 +40,23 @@
 #include "got_lib_object.h"
 
 static const struct got_error *
-diff_blobs(struct got_diffreg_result **resultp,
-struct got_blob_object *blob1, struct got_blob_object *blob2,
+add_line_offset(off_t **line_offsets, size_t *nlines, off_t off)
+{
+	off_t *p;
+
+	p = reallocarray(*line_offsets, *nlines + 1, sizeof(off_t));
+	if (p == NULL)
+		return got_error_from_errno("reallocarray");
+	*line_offsets = p;
+	(*line_offsets)[*nlines] = off;
+	(*nlines)++;
+	return NULL;
+}
+
+static const struct got_error *
+diff_blobs(off_t **line_offsets, size_t *nlines,
+    struct got_diffreg_result **resultp, struct got_blob_object *blob1,
+    struct got_blob_object *blob2,
     const char *label1, const char *label2, mode_t mode1, mode_t mode2,
     int diff_context, int ignore_whitespace, FILE *outfile)
 {
@@ -52,7 +67,12 @@
 	char *idstr1 = NULL, *idstr2 = NULL;
 	size_t size1, size2;
 	struct got_diffreg_result *result;
+	off_t outoff = 0;
+	int n;
 
+	if (line_offsets && *line_offsets && *nlines > 0)
+		outoff = (*line_offsets)[*nlines - 1];
+
 	if (resultp)
 		*resultp = NULL;
 
@@ -116,10 +136,32 @@
 				goto done;
 			}
 		}
-		fprintf(outfile, "blob - %s%s\n", idstr1,
+		n = fprintf(outfile, "blob - %s%s\n", idstr1,
 		    modestr1 ? modestr1 : "");
-		fprintf(outfile, "blob + %s%s\n", idstr2,
+		if (n < 0) {
+			err = got_error_from_errno("fprintf");
+			goto done;
+		}
+		outoff += n;
+		if (line_offsets) {
+			err = add_line_offset(line_offsets, nlines, outoff);
+			if (err)
+				goto done;
+		}
+
+		n = fprintf(outfile, "blob + %s%s\n", idstr2,
 		    modestr2 ? modestr2 : "");
+		if (n < 0) {
+			err = got_error_from_errno("fprintf");
+			goto done;
+		}
+		outoff += n;
+		if (line_offsets) {
+			err = add_line_offset(line_offsets, nlines, outoff);
+			if (err)
+				goto done;
+		}
+
 		free(modestr1);
 		free(modestr2);
 	}
@@ -129,7 +171,7 @@
 		goto done;
 
 	if (outfile) {
-		err = got_diffreg_output(NULL, NULL, result, f1, f2,
+		err = got_diffreg_output(line_offsets, nlines, result, f1, f2,
 		    label1 ? label1 : idstr1,
 		    label2 ? label2 : idstr2,
 		    GOT_DIFF_OUTPUT_UNIDIFF, diff_context, outfile);
@@ -158,21 +200,21 @@
     struct got_object_id *id2, const char *label1, const char *label2,
     mode_t mode1, mode_t mode2, struct got_repository *repo)
 {
-	const struct got_error *err;
 	struct got_diff_blob_output_unidiff_arg *a = arg;
 
-	err = diff_blobs(NULL, blob1, blob2, label1, label2, mode1, mode2,
-	    a->diff_context, a->ignore_whitespace, a->outfile);
-	return err;
+	return diff_blobs(&a->line_offsets, &a->nlines, NULL,
+	    blob1, blob2, label1, label2, mode1, mode2, a->diff_context,
+	    a->ignore_whitespace, a->outfile);
 }
 
 const struct got_error *
-got_diff_blob(struct got_blob_object *blob1, struct got_blob_object *blob2,
+got_diff_blob(off_t **line_offsets, size_t *nlines,
+    struct got_blob_object *blob1, struct got_blob_object *blob2,
     const char *label1, const char *label2, int diff_context,
     int ignore_whitespace, FILE *outfile)
 {
-	return diff_blobs(NULL, blob1, blob2, label1, label2, 0, 0, diff_context,
-	    ignore_whitespace, outfile);
+	return diff_blobs(line_offsets, nlines, NULL, blob1, blob2,
+	    label1, label2, 0, 0, diff_context, ignore_whitespace, outfile);
 }
 
 static const struct got_error *
@@ -259,7 +301,8 @@
 {
 	const struct got_error *err = NULL;
 
-	err = diff_blobs(result, blob1, blob2, NULL, NULL, 0, 0, 3, 0, NULL);
+	err = diff_blobs(NULL, NULL, result, blob1, blob2,
+	    NULL, NULL, 0, 0, 3, 0, NULL);
 	if (err) {
 		got_diffreg_result_free(*result);
 		*result = NULL;
@@ -702,7 +745,8 @@
 }
 
 const struct got_error *
-got_diff_objects_as_blobs(struct got_object_id *id1, struct got_object_id *id2,
+got_diff_objects_as_blobs(off_t **line_offsets, size_t *nlines,
+    struct got_object_id *id1, struct got_object_id *id2,
     const char *label1, const char *label2, int diff_context,
     int ignore_whitespace, struct got_repository *repo, FILE *outfile)
 {
@@ -722,8 +766,8 @@
 		if (err)
 			goto done;
 	}
-	err = got_diff_blob(blob1, blob2, label1, label2, diff_context,
-	    ignore_whitespace, outfile);
+	err = got_diff_blob(line_offsets, nlines, blob1, blob2,
+	    label1, label2, diff_context, ignore_whitespace, outfile);
 done:
 	if (blob1)
 		got_object_blob_close(blob1);
@@ -733,13 +777,15 @@
 }
 
 const struct got_error *
-got_diff_objects_as_trees(struct got_object_id *id1, struct got_object_id *id2,
+got_diff_objects_as_trees(off_t **line_offsets, size_t *nlines,
+    struct got_object_id *id1, struct got_object_id *id2,
     char *label1, char *label2, int diff_context, int ignore_whitespace,
     struct got_repository *repo, FILE *outfile)
 {
 	const struct got_error *err;
 	struct got_tree_object *tree1 = NULL, *tree2 = NULL;
 	struct got_diff_blob_output_unidiff_arg arg;
+	int want_lineoffsets = (line_offsets != NULL && *line_offsets != NULL);
 
 	if (id1 == NULL && id2 == NULL)
 		return got_error(GOT_ERR_NO_OBJ);
@@ -757,8 +803,20 @@
 	arg.diff_context = diff_context;
 	arg.ignore_whitespace = ignore_whitespace;
 	arg.outfile = outfile;
+	if (want_lineoffsets) {
+		arg.line_offsets = *line_offsets;
+		arg.nlines = *nlines;
+	} else {
+		arg.line_offsets = NULL;
+		arg.nlines = 0;
+	}
 	err = got_diff_tree(tree1, tree2, label1, label2, repo,
 	    got_diff_blob_output_unidiff, &arg, 1);
+
+	if (want_lineoffsets) {
+		*line_offsets = arg.line_offsets; /* was likely re-allocated */
+		*nlines = arg.nlines;
+	}
 done:
 	if (tree1)
 		got_object_tree_close(tree1);
@@ -768,8 +826,9 @@
 }
 
 const struct got_error *
-got_diff_objects_as_commits(struct got_object_id *id1,
-    struct got_object_id *id2, int diff_context, int ignore_whitespace,
+got_diff_objects_as_commits(off_t **line_offsets, size_t *nlines,
+    struct got_object_id *id1, struct got_object_id *id2,
+    int diff_context, int ignore_whitespace,
     struct got_repository *repo, FILE *outfile)
 {
 	const struct got_error *err;
@@ -788,7 +847,7 @@
 	if (err)
 		goto done;
 
-	err = got_diff_objects_as_trees(
+	err = got_diff_objects_as_trees(line_offsets, nlines,
 	    commit1 ? got_object_commit_get_tree_id(commit1) : NULL,
 	    got_object_commit_get_tree_id(commit2), "", "", diff_context,
 	    ignore_whitespace, repo, outfile);