diff --git a/src/lib-index/mail-index-map-hdr.c b/src/lib-index/mail-index-map-hdr.c
index eff8a604b8..5f272c5a8c 100644
--- a/src/lib-index/mail-index-map-hdr.c
+++ b/src/lib-index/mail-index-map-hdr.c
@@ -171,7 +171,7 @@ bool mail_index_check_header_compat(struct mail_index *index,
 {
         enum mail_index_header_compat_flags compat_flags = 0;
 
-#if !WORDS_BIGENDIAN
+#ifndef WORDS_BIGENDIAN
 	compat_flags |= MAIL_INDEX_COMPAT_LITTLE_ENDIAN;
 #endif
 
diff --git a/src/lib-index/mail-index-map.c b/src/lib-index/mail-index-map.c
index ed6d23713c..a12814b500 100644
--- a/src/lib-index/mail-index-map.c
+++ b/src/lib-index/mail-index-map.c
@@ -239,7 +239,7 @@ static void mail_index_header_init(struct mail_index *index,
 	hdr->header_size = sizeof(*hdr);
 	hdr->record_size = sizeof(struct mail_index_record);
 
-#if !WORDS_BIGENDIAN
+#ifndef WORDS_BIGENDIAN
 	hdr->compat_flags |= MAIL_INDEX_COMPAT_LITTLE_ENDIAN;
 #endif
 
diff --git a/src/lib-index/mail-transaction-log-file.c b/src/lib-index/mail-transaction-log-file.c
index e33bb1a95c..9239a73ddc 100644
--- a/src/lib-index/mail-transaction-log-file.c
+++ b/src/lib-index/mail-transaction-log-file.c
@@ -536,7 +536,7 @@ mail_transaction_log_file_read_hdr(struct mail_transaction_log_file *file,
 		/* we have compatibility flags */
 		enum mail_index_header_compat_flags compat_flags = 0;
 
-#if !WORDS_BIGENDIAN
+#ifndef WORDS_BIGENDIAN
 		compat_flags |= MAIL_INDEX_COMPAT_LITTLE_ENDIAN;
 #endif
 		if (file->hdr.compat_flags != compat_flags) {
diff --git a/src/lib/byteorder.h b/src/lib/byteorder.h
index b5298580fa..264d397d5d 100644
--- a/src/lib/byteorder.h
+++ b/src/lib/byteorder.h
@@ -244,7 +244,7 @@ static inline uint##size##_t from##size##_to_##to(uint##size##_t x)	\
 	return bswap;							\
 }
 
-#if WORDS_BIGENDIAN
+#ifdef WORDS_BIGENDIAN
 #define __GEN(from, size, to, be, le) ___GEN(from, size, to, be)
 #else
 #define __GEN(from, size, to, be, le) ___GEN(from, size, to, le)
diff --git a/src/lib/sha1.c b/src/lib/sha1.c
index ddbecf2867..fb8247f60a 100644
--- a/src/lib/sha1.c
+++ b/src/lib/sha1.c
@@ -235,7 +235,7 @@ sha1_result(struct sha1_ctxt *ctxt, void *digest0)
 
 	digest = (uint8_t *)digest0;
 	sha1_pad(ctxt);
-#if WORDS_BIGENDIAN
+#ifdef WORDS_BIGENDIAN
 	memmove(digest, &ctxt->h.b8[0], 20);
 #else
 	digest[0] = ctxt->h.b8[3]; digest[1] = ctxt->h.b8[2];
diff --git a/src/lib/test-byteorder.c b/src/lib/test-byteorder.c
index d3fd43820a..9e350ceadb 100644
--- a/src/lib/test-byteorder.c
+++ b/src/lib/test-byteorder.c
@@ -103,7 +103,7 @@ struct unaligned_run {
 	uint32_t le32;
 	uint64_t le64;
 
-#if WORDS_BIGENDIAN
+#ifdef WORDS_BIGENDIAN
 #define cpu8 be8
 #define cpu16 be16
 #define cpu32 be32