diff --git a/arithmetization/src/main/java/net/consensys/linea/zktracer/ZkTracer.java b/arithmetization/src/main/java/net/consensys/linea/zktracer/ZkTracer.java
index cecd10ae..1d949f8b 100644
--- a/arithmetization/src/main/java/net/consensys/linea/zktracer/ZkTracer.java
+++ b/arithmetization/src/main/java/net/consensys/linea/zktracer/ZkTracer.java
@@ -32,7 +32,6 @@
 import net.consensys.linea.config.LineaL1L2BridgeConfiguration;
 import net.consensys.linea.zktracer.module.Module;
 import net.consensys.linea.zktracer.module.hub.Hub;
-import net.consensys.linea.zktracer.opcode.OpCodes;
 import net.consensys.linea.zktracer.types.Utils;
 import org.apache.tuweni.bytes.Bytes;
 import org.hyperledger.besu.datatypes.Hash;
@@ -57,11 +56,12 @@ public class ZkTracer implements ConflationAwareOperationTracer {
 
   static {
     try {
-      // Load opcodes configured in src/main/resources/opcodes.yml.
-      OpCodes.load();
       // Load spillings configured in src/main/resources/spillings.toml.
       spillings = Utils.computeSpillings();
     } catch (final Exception e) {
+      final String errorMsg =
+          "A problem happened during spillings initialization, cause " + e.getCause();
+      log.error(errorMsg);
       throw new RuntimeException(e);
     }
   }
diff --git a/arithmetization/src/main/java/net/consensys/linea/zktracer/opcode/OpCodes.java b/arithmetization/src/main/java/net/consensys/linea/zktracer/opcode/OpCodes.java
index c5c5bef9..3ed4a836 100644
--- a/arithmetization/src/main/java/net/consensys/linea/zktracer/opcode/OpCodes.java
+++ b/arithmetization/src/main/java/net/consensys/linea/zktracer/opcode/OpCodes.java
@@ -20,7 +20,6 @@
 import java.util.List;
 import java.util.Map;
 import java.util.Optional;
-import java.util.concurrent.ConcurrentHashMap;
 import java.util.stream.Collectors;
 
 import com.fasterxml.jackson.databind.JsonNode;
@@ -33,29 +32,31 @@
 public class OpCodes {
   private static final JsonConverter YAML_CONVERTER = JsonConverter.builder().enableYaml().build();
 
-  private static Map<Integer, OpCodeData> valueToOpCodeDataMap = new ConcurrentHashMap<>();
-  private static Map<OpCode, OpCodeData> opCodeToOpCodeDataMap = new ConcurrentHashMap<>();
+  private static Map<Integer, OpCodeData> valueToOpCodeDataMap;
+  private static Map<OpCode, OpCodeData> opCodeToOpCodeDataMap;
+
+  static {
+    /** Loads all opcode metadata from src/main/resources/opcodes.yml. */
+    init();
+  }
 
-  /** Loads all opcode metadata from src/main/resources/opcodes.yml. */
   @SneakyThrows(IOException.class)
-  public static void load() {
-    if (valueToOpCodeDataMap.isEmpty() || opCodeToOpCodeDataMap.isEmpty()) {
-      JsonNode rootNode =
-          YAML_CONVERTER
-              .getObjectMapper()
-              .readTree(OpCodes.class.getClassLoader().getResourceAsStream("opcodes.yml"))
-              .get("opcodes");
+  private static void init() {
+    JsonNode rootNode =
+        YAML_CONVERTER
+            .getObjectMapper()
+            .readTree(OpCodes.class.getClassLoader().getResourceAsStream("opcodes.yml"))
+            .get("opcodes");
 
-      CollectionType typeReference =
-          TypeFactory.defaultInstance().constructCollectionType(List.class, OpCodeData.class);
+    CollectionType typeReference =
+        TypeFactory.defaultInstance().constructCollectionType(List.class, OpCodeData.class);
 
-      List<OpCodeData> opCodes =
-          YAML_CONVERTER.getObjectMapper().treeToValue(rootNode, typeReference);
+    List<OpCodeData> opCodes =
+        YAML_CONVERTER.getObjectMapper().treeToValue(rootNode, typeReference);
 
-      valueToOpCodeDataMap = opCodes.stream().collect(Collectors.toMap(OpCodeData::value, e -> e));
-      opCodeToOpCodeDataMap =
-          opCodes.stream().collect(Collectors.toMap(OpCodeData::mnemonic, e -> e));
-    }
+    valueToOpCodeDataMap = opCodes.stream().collect(Collectors.toMap(OpCodeData::value, e -> e));
+    opCodeToOpCodeDataMap =
+        opCodes.stream().collect(Collectors.toMap(OpCodeData::mnemonic, e -> e));
   }
 
   /**
diff --git a/arithmetization/src/main/java/net/consensys/linea/zktracer/types/Utils.java b/arithmetization/src/main/java/net/consensys/linea/zktracer/types/Utils.java
index 9e68f25d..222c91c7 100644
--- a/arithmetization/src/main/java/net/consensys/linea/zktracer/types/Utils.java
+++ b/arithmetization/src/main/java/net/consensys/linea/zktracer/types/Utils.java
@@ -17,8 +17,8 @@
 
 import java.io.IOException;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.Map;
-import java.util.concurrent.ConcurrentHashMap;
 
 import com.google.common.base.Preconditions;
 import org.apache.tuweni.bytes.Bytes;
@@ -90,7 +90,7 @@ public static BitDecOutput bitDecomposition(int input, int nbStep) {
   }
 
   public static Map<String, Integer> computeSpillings() throws IOException {
-    final Map<String, Integer> spillings = new ConcurrentHashMap<>();
+    final Map<String, Integer> spillings = new HashMap<>();
 
     final TomlTable table =
         Toml.parse(Utils.class.getClassLoader().getResourceAsStream("spillings.toml"))