diff --git a/Documentation/diff-options.adoc b/Documentation/diff-options.adoc
index 9cdad6f72a..fcfcdf0286 100644
--- a/Documentation/diff-options.adoc
+++ b/Documentation/diff-options.adoc
@@ -859,10 +859,18 @@ endif::git-format-patch[]
 	Do not show any source or destination prefix.
 
 `--default-prefix`::
+ifdef::git-format-patch[]
+	Use the default source and destination prefixes ("a/" and "b/").
+	This overrides configuration variables such as `format.noprefix`,
+	`diff.srcPrefix`, `diff.dstPrefix`, and `diff.mnemonicPrefix`
+	(see linkgit:git-config[1]).
+endif::git-format-patch[]
+ifndef::git-format-patch[]
 	Use the default source and destination prefixes ("a/" and "b/").
 	This overrides configuration variables such as `diff.noprefix`,
 	`diff.srcPrefix`, `diff.dstPrefix`, and `diff.mnemonicPrefix`
 	(see linkgit:git-config[1]).
+endif::git-format-patch[]
 
 `--line-prefix=<prefix>`::
 	Prepend an additional _<prefix>_ to every line of output.
diff --git a/builtin/log.c b/builtin/log.c
index 7cb919bca9..89e8b8f011 100644
--- a/builtin/log.c
+++ b/builtin/log.c
@@ -39,6 +39,7 @@
 #include "mailmap.h"
 #include "progress.h"
 #include "commit-slab.h"
+#include "advice.h"
 
 #include "commit-reach.h"
 #include "range-diff.h"
@@ -1095,7 +1096,18 @@ static int git_format_config(const char *var, const char *value,
 		return 0;
 	}
 	if (!strcmp(var, "format.noprefix")) {
-		format_no_prefix = 1;
+		format_no_prefix = git_parse_maybe_bool(value);
+		if (format_no_prefix < 0) {
+			int status = die_message(
+				_("bad boolean config value '%s' for '%s'"),
+				value, var);
+			advise(_("'%s' used to accept any value and "
+				 "treat that as 'true'.\n"
+				 "Now it only accepts boolean values, "
+				 "like what '%s' does.\n"),
+			       var, "diff.noprefix");
+			exit(status);
+		}
 		return 0;
 	}
 
diff --git a/t/t4014-format-patch.sh b/t/t4014-format-patch.sh
index 2135b65cee..bcdb944017 100755
--- a/t/t4014-format-patch.sh
+++ b/t/t4014-format-patch.sh
@@ -2549,10 +2549,26 @@ test_expect_success 'format-patch respects format.noprefix' '
 	grep "^--- blorp" actual
 '
 
+test_expect_success 'format.noprefix=false' '
+	git -c format.noprefix=false format-patch -1 --stdout >actual &&
+	grep "^--- a/blorp" actual
+'
+
 test_expect_success 'format-patch --default-prefix overrides format.noprefix' '
 	git -c format.noprefix \
 		format-patch -1 --default-prefix --stdout >actual &&
 	grep "^--- a/blorp" actual
 '
 
+test_expect_success 'errors on format.noprefix which is not boolean' '
+	cat >expect <<-EOF &&
+	fatal: bad boolean config value ${SQ}not-a-bool${SQ} for ${SQ}format.noprefix${SQ}
+	hint: ${SQ}format.noprefix${SQ} used to accept any value and treat that as ${SQ}true${SQ}.
+	hint: Now it only accepts boolean values, like what ${SQ}diff.noprefix${SQ} does.
+	EOF
+	test_must_fail git -c format.noprefix=not-a-bool \
+		format-patch -1 --stdout 2>actual &&
+	test_cmp expect actual
+'
+
 test_done