diff --git a/libopenfpga/libfpgabitstream/src/bitstream_manager.cpp b/libopenfpga/libfpgabitstream/src/bitstream_manager.cpp
index 07c4c6057..557bca551 100644
--- a/libopenfpga/libfpgabitstream/src/bitstream_manager.cpp
+++ b/libopenfpga/libfpgabitstream/src/bitstream_manager.cpp
@@ -220,6 +220,14 @@ void BitstreamManager::add_child_block(const ConfigBlockId& parent_block, const
   parent_block_ids_[child_block] = parent_block;
 }
 
+void BitstreamManager::reserve_block_bits(const ConfigBlockId& block,
+                                          const size_t& num_bits) {
+  /* Ensure the input ids are valid */
+  VTR_ASSERT(true == valid_block_id(block));
+
+  block_bit_ids_[block].reserve(num_bits);
+}
+
 void BitstreamManager::add_bit_to_block(const ConfigBlockId& block, const ConfigBitId& bit) {
   /* Ensure the input ids are valid */
   VTR_ASSERT(true == valid_block_id(block));
diff --git a/libopenfpga/libfpgabitstream/src/bitstream_manager.h b/libopenfpga/libfpgabitstream/src/bitstream_manager.h
index f94fef472..151f0817a 100644
--- a/libopenfpga/libfpgabitstream/src/bitstream_manager.h
+++ b/libopenfpga/libfpgabitstream/src/bitstream_manager.h
@@ -170,6 +170,10 @@ class BitstreamManager {
     /* Set a block as a child block of another */
     void add_child_block(const ConfigBlockId& parent_block, const ConfigBlockId& child_block);
 
+    /* Reserve a number of configuration bits for a block */
+    void reserve_block_bits(const ConfigBlockId& block,
+                            const size_t& num_bits);
+
     /* Add a configuration bit to a block */
     void add_bit_to_block(const ConfigBlockId& block, const ConfigBitId& bit);
 
diff --git a/openfpga/src/fpga_bitstream/build_grid_bitstream.cpp b/openfpga/src/fpga_bitstream/build_grid_bitstream.cpp
index 33ae3fa4b..577402706 100644
--- a/openfpga/src/fpga_bitstream/build_grid_bitstream.cpp
+++ b/openfpga/src/fpga_bitstream/build_grid_bitstream.cpp
@@ -106,6 +106,7 @@ void build_primitive_bitstream(BitstreamManager& bitstream_manager,
   bitstream_manager.add_child_block(parent_configurable_block, mem_block);
 
   /* Add the bitstream to the bitstream manager */
+  bitstream_manager.reserve_block_bits(mem_block, mode_select_bitstream.size());
   for (const bool& bit : mode_select_bitstream) {
     ConfigBitId config_bit = bitstream_manager.add_bit(bit);
     /* Link the memory bits to the mux mem block */
@@ -214,6 +215,7 @@ void build_physical_block_pin_interc_bitstream(BitstreamManager& bitstream_manag
     VTR_ASSERT(mux_bitstream.size() == module_manager.module_port(mux_mem_module, mux_mem_out_port_id).get_width());
   
     /* Add the bistream to the bitstream manager */
+    bitstream_manager.reserve_block_bits(mux_mem_block, mux_bitstream.size());
     for (const bool& bit : mux_bitstream) {
       ConfigBitId config_bit = bitstream_manager.add_bit(bit);
       /* Link the memory bits to the mux mem block */
@@ -467,6 +469,7 @@ void build_lut_bitstream(BitstreamManager& bitstream_manager,
   bitstream_manager.add_child_block(parent_configurable_block, mem_block);
 
   /* Add the bitstream to the bitstream manager */
+  bitstream_manager.reserve_block_bits(mem_block, lut_bitstream.size());
   for (const bool& bit : lut_bitstream) {
     ConfigBitId config_bit = bitstream_manager.add_bit(bit);
     /* Link the memory bits to the mux mem block */
diff --git a/openfpga/src/fpga_bitstream/build_routing_bitstream.cpp b/openfpga/src/fpga_bitstream/build_routing_bitstream.cpp
index a1df3eeb9..c4dec00db 100644
--- a/openfpga/src/fpga_bitstream/build_routing_bitstream.cpp
+++ b/openfpga/src/fpga_bitstream/build_routing_bitstream.cpp
@@ -98,6 +98,7 @@ void build_switch_block_mux_bitstream(BitstreamManager& bitstream_manager,
   VTR_ASSERT(mux_bitstream.size() == module_manager.module_port(mux_mem_module, mux_mem_out_port_id).get_width());
 
   /* Add the bistream to the bitstream manager */
+  bitstream_manager.reserve_block_bits(mux_mem_block, mux_bitstream.size());
   for (const bool& bit : mux_bitstream) {
     ConfigBitId config_bit = bitstream_manager.add_bit(bit);
     /* Link the memory bits to the mux mem block */
@@ -291,6 +292,7 @@ void build_connection_block_mux_bitstream(BitstreamManager& bitstream_manager,
   VTR_ASSERT(mux_bitstream.size() == module_manager.module_port(mux_mem_module, mux_mem_out_port_id).get_width());
 
   /* Add the bistream to the bitstream manager */
+  bitstream_manager.reserve_block_bits(mux_mem_block, mux_bitstream.size());
   for (const bool& bit : mux_bitstream) {
     ConfigBitId config_bit = bitstream_manager.add_bit(bit);
     /* Link the memory bits to the mux mem block */