diff --git a/src/binfileutils.js b/src/binfileutils.js
index e81ae36..b15b751 100644
--- a/src/binfileutils.js
+++ b/src/binfileutils.js
@@ -63,7 +63,7 @@ export async function endWriteSection(fd) {
     const sectionSize = fd.pos - fd.writingSection.pSectionSize - 8;
     const oldPos = fd.pos;
     fd.pos = fd.writingSection.pSectionSize;
-    fd.writeULE64(sectionSize);
+    await fd.writeULE64(sectionSize);
     fd.pos = oldPos;
     delete fd.writingSection;
 }
diff --git a/src/powersoftau_utils.js b/src/powersoftau_utils.js
index 1475e7e..e998704 100644
--- a/src/powersoftau_utils.js
+++ b/src/powersoftau_utils.js
@@ -25,7 +25,7 @@ export async function writePTauHeader(fd, curve, power, ceremonyPower) {
 
     const oldPos = fd.pos;
 
-    fd.writeULE64(headerSize, pHeaderSize);
+    await fd.writeULE64(headerSize, pHeaderSize);
 
     fd.pos = oldPos;
 }
@@ -287,7 +287,7 @@ export async function writeContributions(fd, curve, contributions) {
 
     const oldPos = fd.pos;
 
-    fd.writeULE64(contributionsSize, pContributionsSize);
+    await fd.writeULE64(contributionsSize, pContributionsSize);
     fd.pos = oldPos;
 }