diff --git a/kk_ihex_write.c b/kk_ihex_write.c
index 9ed8dfd..bf9ae6c 100644
--- a/kk_ihex_write.c
+++ b/kk_ihex_write.c
@@ -10,10 +10,11 @@
 
 #include "kk_ihex_write.h"
 
-static const char IHEX_START = ':';
+#define IHEX_START ':'
+
 static const char IHEX_NEWLINE[] = IHEX_NEWLINE_STRING;
 
-#define ADDRESS_HIGH_MASK 0xFFFF0000U
+#define ADDRESS_HIGH_MASK ((ihex_address_t) 0xFFFF0000U)
 #define ADDRESS_HIGH_BYTES(addr) ((addr) >> 16)
 
 #define HEX_DIGIT(n) ((n) + ( ((n) < 10) ? '0' : ('A' - 10)))
@@ -30,9 +31,9 @@ ihex_init (struct ihex_state * const ihex) {
 #ifndef IHEX_DISABLE_SEGMENTS
     ihex->segment = 0;
 #endif
-    ihex->length = 0;
     ihex->flags = 0;
     ihex->line_length = IHEX_DEFAULT_OUTPUT_LINE_LENGTH;
+    ihex->length = 0;
 }
 
 static char *
@@ -63,18 +64,63 @@ ihex_buffer_newline (char *w) {
     return w;
 }
 
-// Write the contents of the data buffer to w, increment address, and reset
-// data length. Return pointer to one past the last character written to w
-// (w is not NUL-terminated).
+static void
+ihex_write_end_of_file (struct ihex_state * const ihex) {
+    char *w = line_buffer;
+    *w++ = IHEX_START;          // :
+#if 0
+    for (unsigned int i = 7; i; --i) {
+        *w++ = '0';
+    }
+    *w++ = '1';
+    *w++ = 'F';
+    *w++ = 'F';
+#else
+    w = ihex_buffer_byte(w, 0); // length
+    w = ihex_buffer_byte(w, 0); // address msb
+    w = ihex_buffer_byte(w, 0); // address lsb
+    w = ihex_buffer_byte(w, IHEX_END_OF_FILE_RECORD); // record type
+    w = ihex_buffer_byte(w, ~IHEX_END_OF_FILE_RECORD + 1); // checksum
+#endif
+    w = ihex_buffer_newline(w);
+    ihex_flush_buffer(ihex, line_buffer, w);
+}
 
-static char *
-ihex_buffer_data (char *w, struct ihex_state * const ihex) {
+static void
+ihex_write_extended_address (struct ihex_state * const ihex,
+                             const ihex_segment_t address,
+                             const enum ihex_record_type type) {
+    char *w = line_buffer;
+    unsigned int sum = type + 2;
+
+    *w++ = IHEX_START;          // :
+    w = ihex_buffer_byte(w, 2); // length
+    w = ihex_buffer_byte(w, 0); // 16-bit address msb
+    w = ihex_buffer_byte(w, 0); // 16-bit address lsb
+    w = ihex_buffer_byte(w, type); // record type
+    w = ihex_buffer_word(w, address, &sum); // high bytes of address
+    w = ihex_buffer_byte(w, ~sum + 1); // checksum
+    w = ihex_buffer_newline(w);
+    ihex_flush_buffer(ihex, line_buffer, w);
+}
+
+// Write out `ihex->data`
+//
+static void
+ihex_write_data (struct ihex_state * const ihex) {
     unsigned int len = ihex->length;
     unsigned int sum = len;
     uint8_t *r = ihex->data;
+    char *w = line_buffer;
 
     if (!len) {
-        return w;
+        return;
+    }
+
+    if (ihex->flags & IHEX_FLAG_ADDRESS_OVERFLOW) {
+        ihex_write_extended_address(ihex, ADDRESS_HIGH_BYTES(ihex->address),
+                                    IHEX_EXTENDED_LINEAR_ADDRESS_RECORD);
+        ihex->flags &= ~IHEX_FLAG_ADDRESS_OVERFLOW;
     }
 
     // :
@@ -89,7 +135,7 @@ ihex_buffer_data (char *w, struct ihex_state * const ihex) {
         unsigned int addr = ihex->address & 0xFFFFU;
         ihex->address += len;
         if ((0xFFFFU - addr) < len) {
-            // signal overflow (need to write extended address record)
+            // signal address overflow (need to write extended address)
             ihex->flags |= IHEX_FLAG_ADDRESS_OVERFLOW;
         }
         w = ihex_buffer_word(w, addr, &sum);
@@ -107,59 +153,17 @@ ihex_buffer_data (char *w, struct ihex_state * const ihex) {
     } while (--len);
 
     // checksum
-    sum = 0x100U - (sum & 0xFFU);
-    w = ihex_buffer_byte(w, sum);
+    w = ihex_buffer_byte(w, ~sum + 1U);
 
-    return ihex_buffer_newline(w);
-}
-
-static char *
-ihex_buffer_extended_address (char *w, const ihex_segment_t address,
-                              const enum ihex_record_type type) {
-    unsigned int sum = type + 2;
-
-    *w++ = IHEX_START;          // :
-    w = ihex_buffer_byte(w, 2); // length
-    w = ihex_buffer_byte(w, 0); // address msb
-    w = ihex_buffer_byte(w, 0); // address lsb
-    w = ihex_buffer_byte(w, type); // record type
-    w = ihex_buffer_word(w, address, &sum); // high bytes of 32-bit address
-    w = ihex_buffer_byte(w, 0x100U - sum); // checksum
-    return ihex_buffer_newline(w);
-}
-
-// Write an end of file record to w, return a pointer to one past the
-// last character written to w (which is not NUL-terminated).
-
-static char *
-ihex_buffer_end_of_file (char *w) {
-    *w++ = IHEX_START;          // :
-    w = ihex_buffer_byte(w, 0); // length
-    w = ihex_buffer_byte(w, 0); // address msb
-    w = ihex_buffer_byte(w, 0); // address lsb
-    w = ihex_buffer_byte(w, IHEX_END_OF_FILE_RECORD); // record type
-    w = ihex_buffer_byte(w, 0x100U - IHEX_END_OF_FILE_RECORD); // checksum
-    return ihex_buffer_newline(w);
-}
-
-static void
-ihex_check_address_overflow (struct ihex_state *ihex) {
-    if (ihex->flags & IHEX_FLAG_ADDRESS_OVERFLOW) {
-        char *w = ihex_buffer_extended_address(line_buffer,
-                    ADDRESS_HIGH_BYTES(ihex->address),
-                    IHEX_EXTENDED_LINEAR_ADDRESS_RECORD);
-        ihex_flush_buffer(ihex, line_buffer, w);
-        ihex->flags &= ~IHEX_FLAG_ADDRESS_OVERFLOW;
-    }
+    w = ihex_buffer_newline(w);
+    ihex_flush_buffer(ihex, line_buffer, w);
 }
 
 void
 ihex_write_at_address (struct ihex_state *ihex, ihex_address_t address) {
     if (ihex->length) {
-        ihex_check_address_overflow(ihex);
         // flush any existing data
-        char *w = ihex_buffer_data(line_buffer, ihex);
-        ihex_flush_buffer(ihex, line_buffer, w);
+        ihex_write_data(ihex);
     }
     if ((ihex->address & ADDRESS_HIGH_MASK) != (address & ADDRESS_HIGH_MASK)) {
         ihex->flags |= IHEX_FLAG_ADDRESS_OVERFLOW;
@@ -186,42 +190,32 @@ ihex_write_at_segment (struct ihex_state *ihex, ihex_segment_t segment, ihex_add
     ihex_write_at_address(ihex, address);
     if (ihex->segment != segment) {
         // clear segment
-        char *w = ihex_buffer_extended_address(line_buffer,
-                    (ihex->segment = segment),
-                    IHEX_EXTENDED_SEGMENT_ADDRESS_RECORD);
-        ihex_flush_buffer(ihex, line_buffer, w);
+        ihex_write_extended_address(ihex, (ihex->segment = segment),
+                                    IHEX_EXTENDED_SEGMENT_ADDRESS_RECORD);
     }
 }
 #endif
 
 void
-ihex_write_byte (struct ihex_state *ihex, uint8_t byte) {
-    ihex->data[(ihex->length)++] = byte;
-    if (ihex->length >= ihex->line_length) {
-        ihex_check_address_overflow(ihex);
-        char *w = ihex_buffer_data(line_buffer, ihex);
-        ihex_flush_buffer(ihex, line_buffer, w);
+ihex_write_byte (struct ihex_state *ihex, unsigned int byte) {
+    if (ihex->line_length <= ihex->length) {
+        ihex_write_data(ihex);
     }
+    ihex->data[(ihex->length)++] = byte;
 }
 
 void
 ihex_end_write (struct ihex_state *ihex) {
-    char *w;
-    if (ihex->length) {
-        ihex_check_address_overflow(ihex);
-        w = ihex_buffer_data(line_buffer, ihex);
-        ihex_flush_buffer(ihex, line_buffer, w);
-    }
-    w = ihex_buffer_end_of_file(line_buffer);
-    ihex_flush_buffer(ihex, line_buffer, w);
+    ihex_write_data(ihex); // flush any remaining data
+    ihex_write_end_of_file(ihex);
 }
 
 void
 ihex_write_bytes (struct ihex_state *ihex, uint8_t *data, unsigned int count) {
     uint8_t *r = data;
     while (count) {
-        unsigned int i = ihex->line_length - ihex->length;
-        if (i) {
+        if (ihex->line_length > ihex->length) {
+            unsigned int i = ihex->line_length - ihex->length;
             uint8_t *w = &(ihex->data[ihex->length]);
             i = (i > count) ? count : i;
             count -= i;
@@ -229,13 +223,9 @@ ihex_write_bytes (struct ihex_state *ihex, uint8_t *data, unsigned int count) {
             do {
                 *w++ = *r++;
             } while (--i);
+        } else {
+            ihex_write_data(ihex);
         }
-        if (ihex->length >= ihex->line_length) {
-            char *w;
-            ihex_check_address_overflow(ihex);
-             w = ihex_buffer_data(line_buffer, ihex);
-            ihex_flush_buffer(ihex, line_buffer, w);
-        }
-    } while (count);
+    }
 }
 
diff --git a/kk_ihex_write.h b/kk_ihex_write.h
index 0417578..f5621d0 100644
--- a/kk_ihex_write.h
+++ b/kk_ihex_write.h
@@ -91,7 +91,7 @@ void ihex_init(struct ihex_state * const ihex);
 void ihex_write_at_address(struct ihex_state *ihex, ihex_address_t address);
 
 // Write a single byte
-void ihex_write_byte(struct ihex_state *ihex, uint8_t b);
+void ihex_write_byte(struct ihex_state *ihex, unsigned int b);
 
 // Write `count` bytes from `data`
 void ihex_write_bytes(struct ihex_state *ihex, uint8_t *data, unsigned int count);