diff --git a/rom_usage.awk b/rom_usage.awk
index bcc2f26..78919cf 100644
--- a/rom_usage.awk
+++ b/rom_usage.awk
@@ -1,10 +1,32 @@
 # Pipe main.map into this to get ROM size info.
 
-/^CODE/ { code_start = ("0x" $2) + 0 }
+# https://stackoverflow.com/a/32437561/211234
+function parse_hex(hex_string) {
+    if (hex_string ~ /^0x/) {
+        hex_string = substr(hex_string, 3)
+    }
 
-/^RODATA/ { rodata_end = ("0x" $3) + 0 }
+    value = 0
+    for (i = 1; i <= length(hex_string); i++) {
+        value = value*16 + H[substr(hex_string, i, 1)]
+    }
 
-/^VECTORS/ { vectors_start = ("0x" $2) + 0 }
+    return value
+}
+
+BEGIN {
+    # Build map from hex digit to value.
+    for (i = 0; i < 16; i++) {
+        H[sprintf("%x",i)] = i
+        H[sprintf("%X",i)] = i
+    }
+}
+
+/^CODE/ { code_start = parse_hex($2) }
+
+/^RODATA/ { rodata_end = parse_hex($3) }
+
+/^VECTORS/ { vectors_start = parse_hex($2) }
 
 END {
     code = rodata_end - code_start + 1