diff --git a/Documentation/config.txt b/Documentation/config.txt
index ab641bf5a9..abf07be7b6 100644
--- a/Documentation/config.txt
+++ b/Documentation/config.txt

@@ -919,6 +919,12 @@ core.abbrev::
        in your repository, which hopefully is enough for
        abbreviated object names to stay unique for some time.
        The minimum length is 4.
++
+This can also be set to relative values such as `+2` or `-2`, which
+means to add or subtract N characters from the SHA-1 that Git would
+otherwise print, this allows for producing more future-proof SHA-1s
+for use within a given project, while adjusting the value for the
+current approximate number of objects.

diff --git a/Documentation/diff-options.txt b/Documentation/diff-options.txt
index f466600972..f1114a7b8d 100644
--- a/Documentation/diff-options.txt
+++ b/Documentation/diff-options.txt

@@ -384,6 +384,9 @@ endif::git-format-patch[]
        independent of the `--full-index` option above, which controls
        the diff-patch output format.  Non default number of
        digits can be specified with `--abbrev=<n>`.
++
+Can also be set to a relative value, see `core.abbrev` in
+linkgit:git-diff[1].

diff --git a/config.c b/config.c
index 12f762ad92..cd95c6bdfb 100644
--- a/config.c
+++ b/config.c

@@ -1151,6 +1151,17 @@ static int git_default_core_config(const char *var, const char *value)
                        return config_error_nonbool(var);
                if (!strcasecmp(value, "auto")) {
                        default_abbrev = -1;
+               } else if (*value == '+' || *value == '-') {
+                       int relative = git_config_int(var, value);
+                       if (relative == 0)
+                               die(_("bad core.abbrev value %s. "

+                                     "relative values must be non-zero"),
+                                   value);
+                       if (abs(relative) > GIT_SHA1_HEXSZ)
+                               die(_("bad core.abbrev value %s. "
+                                     "impossibly out of range"),
+                                   value);
+                       default_abbrev_relative = relative;
                } else {
                        int abbrev = git_config_int(var, value);
                        if (abbrev < minimum_abbrev || abbrev > 40)

diff --git a/diff.c b/diff.c
index e0141cfbc0..f7861b8472 100644
--- a/diff.c
+++ b/diff.c

@@ -4801,16 +4801,28 @@ int diff_opt_parse(struct diff_options *options,
        else if (!strcmp(arg, "--abbrev"))
                options->abbrev = DEFAULT_ABBREV;
        else if (skip_prefix(arg, "--abbrev=", &arg)) {
+               int v;
                char *end;
                if (!strcmp(arg, ""))
                        die("--abbrev expects a value, got '%s'", arg);
-               options->abbrev = strtoul(arg, &end, 10);
+               v = strtoul(arg, &end, 10);
                if (*end)
                        die("--abbrev expects a numerical value, got '%s'", arg);
-               if (options->abbrev < MINIMUM_ABBREV) {
+               if (*arg == '+' || *arg == '-') {
+                       if (v == 0) {
+                               die("relative abbrev must be non-zero");
+                       } else if (abs(v) > the_hash_algo->hexsz) {
+                               die("relative abbrev impossibly out of range");
+                       } else {
+                               default_abbrev_relative = v;
+                               options->abbrev = DEFAULT_ABBREV;
+                       }
+               } else if (v < MINIMUM_ABBREV) {
                        options->abbrev = MINIMUM_ABBREV;
-               } else if (the_hash_algo->hexsz < options->abbrev) {
+               } else if (the_hash_algo->hexsz < v) {
                        options->abbrev = the_hash_algo->hexsz;
+               } else {
+                       options->abbrev = v;