diff --git a/gpt.cc b/gpt.cc
index 848340b..76cd9ad 100644
--- a/gpt.cc
+++ b/gpt.cc
@@ -80,6 +80,7 @@ GPTData::GPTData(void) {
    beQuiet = 0;
    whichWasUsed = use_new;
    mainHeader.numParts = 0;
+   mainHeader.lastUsableLBA = 0;
    numParts = 0;
    SetGPTSize(NUM_GPT_ENTRIES);
    // Initialize CRC functions...
@@ -143,6 +144,7 @@ GPTData::GPTData(string filename) {
    beQuiet = 0;
    whichWasUsed = use_new;
    mainHeader.numParts = 0;
+   mainHeader.lastUsableLBA = 0;
    numParts = 0;
    // Initialize CRC functions...
    chksum_crc32gentab();