diff --git a/src/repart/repart.c b/src/repart/repart.c
index cf4f670401..5ba535e032 100644
--- a/src/repart/repart.c
+++ b/src/repart/repart.c
@@ -100,9 +100,6 @@
 /* We know up front we're never going to put more than this in a verity sig partition. */
 #define VERITY_SIG_SIZE (HARD_MIN_SIZE*4ULL)
 
-/* libfdisk takes off slightly more than 1M of the disk size when creating a GPT disk label */
-#define GPT_METADATA_SIZE (1044ULL*1024ULL)
-
 /* LUKS2 takes off 16M of the partition size with its metadata by default */
 #define LUKS2_METADATA_SIZE (16ULL*1024ULL*1024ULL)
 
@@ -11250,12 +11247,26 @@ static int determine_auto_size(
 
         assert(c);
 
-        minimal_size = round_up_size(GPT_METADATA_SIZE, 4096);
+        /* At the beginning of the image, some size is reserved for:
+         * Protective MBR (1 block) + GPT header (1 block) +
+         * Primary partition table (minimum 16KiB) = (2 * c->sector_size) + (16 * 1024)
+         *
+         * Note that fdisk usually sets the first usable block to 1MiB (at least for
+         * disks larger than 4MiB), so we just force it to that as well. If fdisk
+         * decides to set it lower, we made the image a bit larger than necessary,
+         * if it sets it higher, we'd have a problem. */
+        minimal_size = 1024 * 1024;
+        /* Of course need to align the start to our grain size as well */
+        minimal_size = round_up_size(minimal_size, c->grain_size);
+
+        /* At the end of the image, there is size reserved for:
+         * Secondary partition table (minimum 16KiB) + GPT header (1 block) */
+        minimal_size += (16 * 1024) + c->sector_size;
 
         if (c->from_scratch)
                 current_size = 0;
         else
-                current_size = round_up_size(GPT_METADATA_SIZE, 4096);
+                current_size = minimal_size;
 
         foreign_size = 0;
 
diff --git a/test/units/TEST-58-REPART.sh b/test/units/TEST-58-REPART.sh
index bd33e93d59..9970dac662 100755
--- a/test/units/TEST-58-REPART.sh
+++ b/test/units/TEST-58-REPART.sh
@@ -370,7 +370,7 @@ label-id: 1D2CE291-7CCE-4F7D-BC83-FDB49AD74EBD
 device: $imgs/zzz
 unit: sectors
 first-lba: 2048
-last-lba: 6422494
+last-lba: 6422487
 $imgs/zzz1 : start=        2048, size=      591856, type=933AC7E1-2EB4-4F13-B844-0E14E2AEF915, uuid=4980595D-D74A-483A-AA9E-9903879A0EE5, name=\"home-first\", attrs=\"GUID:59\"
 $imgs/zzz2 : start=      593904, size=      591856, type=${root_guid}, uuid=${root_uuid}, name=\"root-${architecture}\", attrs=\"GUID:59\"
 $imgs/zzz3 : start=     1185760, size=      591864, type=${root_guid}, uuid=${root_uuid2}, name=\"root-${architecture}-2\", attrs=\"GUID:59\"
@@ -434,7 +434,7 @@ label-id: 1D2CE291-7CCE-4F7D-BC83-FDB49AD74EBD
 device: $imgs/zzz
 unit: sectors
 first-lba: 2048
-last-lba: 6553566
+last-lba: 6553559
 $imgs/zzz1 : start=        2048, size=      591856, type=933AC7E1-2EB4-4F13-B844-0E14E2AEF915, uuid=4980595D-D74A-483A-AA9E-9903879A0EE5, name=\"home-first\", attrs=\"GUID:59\"
 $imgs/zzz2 : start=      593904, size=      591856, type=${root_guid}, uuid=${root_uuid}, name=\"root-${architecture}\", attrs=\"GUID:59\"
 $imgs/zzz3 : start=     1185760, size=      591864, type=${root_guid}, uuid=${root_uuid2}, name=\"root-${architecture}-2\", attrs=\"GUID:59\"
@@ -568,6 +568,51 @@ EOF
     assert_in "$imgs/copy_to3 : start=       32768, size=       90072, type=${esp_guid}," "$output"
 }
 
+testcase_size_auto_with_grain_size() {
+    local defs imgs output
+
+    defs="$(mktemp --directory "/tmp/test-repart.defs.XXXXXXXXXX")"
+    imgs="$(mktemp --directory "/var/tmp/test-repart.imgs.XXXXXXXXXX")"
+    # shellcheck disable=SC2064
+    trap "rm -rf '$defs' '$imgs'" RETURN
+    chmod 0755 "$defs"
+
+    tee "$defs/01-esp.conf" <<EOF
+[Partition]
+Type=esp
+SizeMinBytes=10M
+EOF
+
+    tee "$defs/02-usr.conf" <<EOF
+[Partition]
+Type=usr-${architecture}
+SizeMinBytes=10M
+EOF
+
+    tee "$defs/03-root.conf" <<EOF
+[Partition]
+Type=root-${architecture}
+SizeMinBytes=10M
+EOF
+
+    systemd-repart --offline="$OFFLINE" \
+                   --empty=create \
+                   --size=auto \
+                   --definitions="$defs" \
+                   --seed="$seed" \
+                   --dry-run=no \
+                   --grain-size=2097152 \
+                   "$imgs/auto"
+
+    output=$(sfdisk --dump "$imgs/auto")
+
+    assert_in "first-lba: 2048" "$output"
+    assert_in "last-lba: 65535" "$output"
+    assert_in "$imgs/auto1 : start=        4096, size=       20480, type=${esp_guid}," "$output"
+    assert_in "$imgs/auto2 : start=       24576, size=       20480, type=${usr_guid}," "$output"
+    assert_in "$imgs/auto3 : start=       45056, size=       20480, type=${root_guid}," "$output"
+}
+
 testcase_dropin() {
     local defs imgs output