diff --git a/src/home/homework-luks.c b/src/home/homework-luks.c
index 3d3369f299..39ad56808d 100644
--- a/src/home/homework-luks.c
+++ b/src/home/homework-luks.c
@@ -141,17 +141,19 @@ static int probe_file_system_by_fd(
         errno = 0;
         r = blkid_probe_set_device(b, fd, 0, 0);
         if (r != 0)
-                return errno > 0 ? -errno : -ENOMEM;
+                return errno_or_else(ENOMEM);
 
         (void) blkid_probe_enable_superblocks(b, 1);
         (void) blkid_probe_set_superblocks_flags(b, BLKID_SUBLKS_TYPE|BLKID_SUBLKS_UUID);
 
         errno = 0;
         r = blkid_do_safeprobe(b);
-        if (IN_SET(r, -2, 1)) /* nothing found or ambiguous result */
+        if (r == _BLKID_SAFEPROBE_ERROR)
+                return errno_or_else(EIO);
+        if (IN_SET(r, _BLKID_SAFEPROBE_AMBIGUOUS, _BLKID_SAFEPROBE_NOT_FOUND))
                 return -ENOPKG;
-        if (r != 0)
-                return errno > 0 ? -errno : -EIO;
+
+        assert(r == _BLKID_SAFEPROBE_FOUND);
 
         (void) blkid_probe_lookup_value(b, "TYPE", &fstype, NULL);
         if (!fstype)
@@ -656,7 +658,7 @@ static int luks_validate(
         errno = 0;
         r = blkid_probe_set_device(b, fd, 0, 0);
         if (r != 0)
-                return errno > 0 ? -errno : -ENOMEM;
+                return errno_or_else(ENOMEM);
 
         (void) blkid_probe_enable_superblocks(b, 1);
         (void) blkid_probe_set_superblocks_flags(b, BLKID_SUBLKS_TYPE);
@@ -665,10 +667,12 @@ static int luks_validate(
 
         errno = 0;
         r = blkid_do_safeprobe(b);
-        if (IN_SET(r, -2, 1)) /* nothing found or ambiguous result */
+        if (r == _BLKID_SAFEPROBE_ERROR)
+                return errno_or_else(EIO);
+        if (IN_SET(r, _BLKID_SAFEPROBE_AMBIGUOUS, _BLKID_SAFEPROBE_NOT_FOUND))
                 return -ENOPKG;
-        if (r != 0)
-                return errno > 0 ? -errno : -EIO;
+
+        assert(r == _BLKID_SAFEPROBE_FOUND);
 
         (void) blkid_probe_lookup_value(b, "TYPE", &fstype, NULL);
         if (streq_ptr(fstype, "crypto_LUKS")) {
@@ -687,12 +691,12 @@ static int luks_validate(
         errno = 0;
         pl = blkid_probe_get_partitions(b);
         if (!pl)
-                return errno > 0 ? -errno : -ENOMEM;
+                return errno_or_else(ENOMEM);
 
         errno = 0;
         n = blkid_partlist_numof_partitions(pl);
         if (n < 0)
-                return errno > 0 ? -errno : -EIO;
+                return errno_or_else(EIO);
 
         for (int i = 0; i < n; i++) {
                 sd_id128_t id = SD_ID128_NULL;
@@ -701,7 +705,7 @@ static int luks_validate(
                 errno = 0;
                 pp = blkid_partlist_get_partition(pl, i);
                 if (!pp)
-                        return errno > 0 ? -errno : -EIO;
+                        return errno_or_else(EIO);
 
                 if (sd_id128_string_equal(blkid_partition_get_type_string(pp), SD_GPT_USER_HOME) <= 0)
                         continue;
diff --git a/src/partition/repart.c b/src/partition/repart.c
index ce65ead62a..46b68c730c 100644
--- a/src/partition/repart.c
+++ b/src/partition/repart.c
@@ -4840,12 +4840,14 @@ static int resolve_copy_blocks_auto_candidate(
 
         errno = 0;
         r = blkid_do_safeprobe(b);
-        if (IN_SET(r, -2, 1)) { /* nothing found or ambiguous result */
+        if (r == _BLKID_SAFEPROBE_ERROR)
+                return log_error_errno(errno_or_else(EIO), "Unable to probe for partition table of '%s': %m", p);
+        if (IN_SET(r, _BLKID_SAFEPROBE_AMBIGUOUS, _BLKID_SAFEPROBE_NOT_FOUND)) {
                 log_debug("Didn't find partition table on block device '%s'.", p);
                 return false;
         }
-        if (r != 0)
-                return log_error_errno(errno_or_else(EIO), "Unable to probe for partition table of '%s': %m", p);
+
+        assert(r == _BLKID_SAFEPROBE_FOUND);
 
         (void) blkid_probe_lookup_value(b, "PTTYPE", &pttype, NULL);
         if (!streq_ptr(pttype, "gpt")) {
@@ -4857,7 +4859,6 @@ static int resolve_copy_blocks_auto_candidate(
         pl = blkid_probe_get_partitions(b);
         if (!pl)
                 return log_error_errno(errno_or_else(EIO), "Unable read partition table of '%s': %m", p);
-        errno = 0;
 
         pp = blkid_partlist_devno_to_partition(pl, partition_devno);
         if (!pp) {
diff --git a/src/shared/blkid-util.h b/src/shared/blkid-util.h
index d4e78627b8..abc4b6166d 100644
--- a/src/shared/blkid-util.h
+++ b/src/shared/blkid-util.h
@@ -34,4 +34,14 @@ static inline int blkid_partition_get_type_id128(blkid_partition p, sd_id128_t *
 
         return sd_id128_from_string(s, ret);
 }
+
+/* Define symbolic names for blkid_do_safeprobe() return values, since blkid only uses literal numbers. We
+ * prefix these symbolic definitions with underscores, to not invade libblkid's namespace needlessly. */
+enum {
+        _BLKID_SAFEPROBE_FOUND     =  0,
+        _BLKID_SAFEPROBE_NOT_FOUND =  1,
+        _BLKID_SAFEPROBE_AMBIGUOUS = -2,
+        _BLKID_SAFEPROBE_ERROR     = -1,
+};
+
 #endif
diff --git a/src/shared/dissect-image.c b/src/shared/dissect-image.c
index 9ce9775049..cf7fae76d1 100644
--- a/src/shared/dissect-image.c
+++ b/src/shared/dissect-image.c
@@ -119,14 +119,16 @@ int probe_filesystem_full(int fd, const char *path, char **ret_fstype) {
 
         errno = 0;
         r = blkid_do_safeprobe(b);
-        if (r == 1)
+        if (r == _BLKID_SAFEPROBE_NOT_FOUND)
                 goto not_found;
-        if (r == -2)
+        if (r == _BLKID_SAFEPROBE_AMBIGUOUS)
                 return log_debug_errno(SYNTHETIC_ERRNO(EUCLEAN),
                                        "Results ambiguous for partition %s", path);
-        if (r != 0)
+        if (r == _BLKID_SAFEPROBE_ERROR)
                 return log_debug_errno(errno_or_else(EIO), "Failed to probe partition %s: %m", path);
 
+        assert(r == _BLKID_SAFEPROBE_FOUND);
+
         (void) blkid_probe_lookup_value(b, "TYPE", &fstype, NULL);
 
         if (fstype) {
@@ -439,10 +441,12 @@ static int dissect_image(
 
         errno = 0;
         r = blkid_do_safeprobe(b);
-        if (IN_SET(r, -2, 1))
-                return log_debug_errno(SYNTHETIC_ERRNO(ENOPKG), "Failed to identify any partition table.");
-        if (r != 0)
+        if (r == _BLKID_SAFEPROBE_ERROR)
                 return errno_or_else(EIO);
+        if (IN_SET(r, _BLKID_SAFEPROBE_AMBIGUOUS, _BLKID_SAFEPROBE_NOT_FOUND))
+                return log_debug_errno(SYNTHETIC_ERRNO(ENOPKG), "Failed to identify any partition table.");
+
+        assert(r == _BLKID_SAFEPROBE_FOUND);
 
         if ((!(flags & DISSECT_IMAGE_GPT_ONLY) &&
             (flags & DISSECT_IMAGE_GENERIC_ROOT)) ||
diff --git a/src/shared/find-esp.c b/src/shared/find-esp.c
index fa234c8b5f..e019b81620 100644
--- a/src/shared/find-esp.c
+++ b/src/shared/find-esp.c
@@ -564,19 +564,21 @@ static int verify_xbootldr_blkid(
         errno = 0;
         b = blkid_new_probe_from_filename(node);
         if (!b)
-                return log_error_errno(errno ?: SYNTHETIC_ERRNO(ENOMEM), "%s: Failed to create blkid probe: %m", node);
+                return log_error_errno(errno_or_else(ENOMEM), "%s: Failed to create blkid probe: %m", node);
 
         blkid_probe_enable_partitions(b, 1);
         blkid_probe_set_partitions_flags(b, BLKID_PARTS_ENTRY_DETAILS);
 
         errno = 0;
         r = blkid_do_safeprobe(b);
-        if (r == -2)
+        if (r == _BLKID_SAFEPROBE_AMBIGUOUS)
                 return log_error_errno(SYNTHETIC_ERRNO(ENODEV), "%s: File system is ambiguous.", node);
-        else if (r == 1)
+        if (r == _BLKID_SAFEPROBE_NOT_FOUND)
                 return log_error_errno(SYNTHETIC_ERRNO(ENODEV), "%s: File system does not contain a label.", node);
-        else if (r != 0)
-                return log_error_errno(errno ?: SYNTHETIC_ERRNO(EIO), "%s: Failed to probe file system: %m", node);
+        if (r == _BLKID_SAFEPROBE_ERROR)
+                return log_error_errno(errno_or_else(EIO), "%s: Failed to probe file system: %m", node);
+
+        assert(r == _BLKID_SAFEPROBE_FOUND);
 
         r = blkid_probe_lookup_value(b, "PART_ENTRY_SCHEME", &type, NULL);
         if (r != 0)
@@ -588,7 +590,7 @@ static int verify_xbootldr_blkid(
                 errno = 0;
                 r = blkid_probe_lookup_value(b, "PART_ENTRY_TYPE", &v, NULL);
                 if (r != 0)
-                        return log_error_errno(errno ?: SYNTHETIC_ERRNO(EIO), "%s: Failed to probe PART_ENTRY_TYPE: %m", node);
+                        return log_error_errno(errno_or_else(EIO), "%s: Failed to probe PART_ENTRY_TYPE: %m", node);
                 if (sd_id128_string_equal(v, SD_GPT_XBOOTLDR) <= 0)
                         return log_full_errno(searching ? LOG_DEBUG : LOG_ERR,
                                               searching ? SYNTHETIC_ERRNO(EADDRNOTAVAIL) : SYNTHETIC_ERRNO(ENODEV),
@@ -597,7 +599,7 @@ static int verify_xbootldr_blkid(
                 errno = 0;
                 r = blkid_probe_lookup_value(b, "PART_ENTRY_UUID", &v, NULL);
                 if (r != 0)
-                        return log_error_errno(errno ?: SYNTHETIC_ERRNO(EIO), "%s: Failed to probe PART_ENTRY_UUID: %m", node);
+                        return log_error_errno(errno_or_else(EIO), "%s: Failed to probe PART_ENTRY_UUID: %m", node);
                 r = sd_id128_from_string(v, &uuid);
                 if (r < 0)
                         return log_error_errno(r, "%s: Partition has invalid UUID PART_ENTRY_TYPE=%s: %m", node, v);
@@ -607,7 +609,7 @@ static int verify_xbootldr_blkid(
                 errno = 0;
                 r = blkid_probe_lookup_value(b, "PART_ENTRY_TYPE", &v, NULL);
                 if (r != 0)
-                        return log_error_errno(errno ?: SYNTHETIC_ERRNO(EIO), "%s: Failed to probe PART_ENTRY_TYPE: %m", node);
+                        return log_error_errno(errno_or_else(EIO), "%s: Failed to probe PART_ENTRY_TYPE: %m", node);
                 if (!streq(v, "0xea"))
                         return log_full_errno(searching ? LOG_DEBUG : LOG_ERR,
                                               searching ? SYNTHETIC_ERRNO(EADDRNOTAVAIL) : SYNTHETIC_ERRNO(ENODEV),