diff --git a/src/libawkward/builder/ArrayBuilder.cpp b/src/libawkward/builder/ArrayBuilder.cpp
index f3c1719efd..d1816b2a80 100644
--- a/src/libawkward/builder/ArrayBuilder.cpp
+++ b/src/libawkward/builder/ArrayBuilder.cpp
@@ -29,7 +29,9 @@ namespace awkward {
 
   void
   ArrayBuilder::clear() {
-    builder_.get()->clear();
+    if (builder_) {
+      builder_.get()->clear();
+    }
   }
 
   void
diff --git a/src/libawkward/builder/BoolBuilder.cpp b/src/libawkward/builder/BoolBuilder.cpp
index ccf26a8f1c..a52e4001b8 100644
--- a/src/libawkward/builder/BoolBuilder.cpp
+++ b/src/libawkward/builder/BoolBuilder.cpp
@@ -34,7 +34,7 @@ namespace awkward {
 
     container.copy_buffer(form_key.str() + "-data",
                           buffer_.ptr().get(),
-                          buffer_.length() * (int64_t)sizeof(bool));
+                          (int64_t)(buffer_.length() * sizeof(bool)));
 
     return "{\"class\": \"NumpyArray\", \"primitive\": \"bool\", \"form_key\": \""
            + form_key.str() + "\"}";
diff --git a/src/libawkward/builder/GrowableBuffer.cpp b/src/libawkward/builder/GrowableBuffer.cpp
index de918d9722..a4d373723b 100644
--- a/src/libawkward/builder/GrowableBuffer.cpp
+++ b/src/libawkward/builder/GrowableBuffer.cpp
@@ -128,7 +128,7 @@ namespace awkward {
   GrowableBuffer<T>::clear() {
     length_ = 0;
     reserved_ = (size_t) options_.initial();
-    ptr_ = nullptr;
+    ptr_ = UniquePtr(reinterpret_cast<T*>(awkward_malloc(options_.initial()*(int64_t)sizeof(T))));
   }
 
   template <typename T>