diff --git a/src/main/java/org/apache/xml/security/stax/impl/stax/XMLSecNamespaceImpl.java b/src/main/java/org/apache/xml/security/stax/impl/stax/XMLSecNamespaceImpl.java
index 7bba770..1673eed 100644
--- a/src/main/java/org/apache/xml/security/stax/impl/stax/XMLSecNamespaceImpl.java
+++ b/src/main/java/org/apache/xml/security/stax/impl/stax/XMLSecNamespaceImpl.java
@@ -26,6 +26,7 @@
 import javax.xml.stream.XMLStreamException;
 import java.io.IOException;
 import java.io.Writer;
+import java.util.Collections;
 import java.util.Map;
 import java.util.WeakHashMap;
 
@@ -35,8 +36,8 @@
  */
 public final class XMLSecNamespaceImpl extends XMLSecEventBaseImpl implements XMLSecNamespace {
 
-    private static final Map<String, Map<String, XMLSecNamespace>> xmlSecNamespaceMap =
-            new WeakHashMap<>();
+    private static final Map<String, Map<String, XMLSecNamespace>> XMLSEC_NS_MAP =
+            Collections.synchronizedMap(new WeakHashMap<String, Map<String, XMLSecNamespace>>());
 
     private String prefix;
     private final String uri;
@@ -57,7 +58,7 @@
         if (uriToUse == null) {
             uriToUse = "";
         }
-        Map<String, XMLSecNamespace> nsMap = xmlSecNamespaceMap.get(prefixToUse);
+        Map<String, XMLSecNamespace> nsMap = XMLSEC_NS_MAP.get(prefixToUse);
         if (nsMap != null) {
             XMLSecNamespace xmlSecNamespace = nsMap.get(uriToUse);
             if (xmlSecNamespace != null) {
@@ -71,7 +72,7 @@
             nsMap = new WeakHashMap<>();
             XMLSecNamespace xmlSecNamespace = new XMLSecNamespaceImpl(prefixToUse, uriToUse);
             nsMap.put(uriToUse, xmlSecNamespace);
-            xmlSecNamespaceMap.put(prefixToUse, nsMap);
+            XMLSEC_NS_MAP.put(prefixToUse, nsMap);
             return xmlSecNamespace;
         }
     }
diff --git a/src/main/java/org/apache/xml/security/stax/impl/transformer/canonicalizer/CanonicalizerBase.java b/src/main/java/org/apache/xml/security/stax/impl/transformer/canonicalizer/CanonicalizerBase.java
index ade9046..77e3e66 100644
--- a/src/main/java/org/apache/xml/security/stax/impl/transformer/canonicalizer/CanonicalizerBase.java
+++ b/src/main/java/org/apache/xml/security/stax/impl/transformer/canonicalizer/CanonicalizerBase.java
@@ -80,7 +80,7 @@
         NODE_AFTER_DOCUMENT_ELEMENT
     }
 
-    private static final Map<String, byte[]> cache = new WeakHashMap<>();
+    private static final Map<String, byte[]> CACHE = Collections.synchronizedMap(new WeakHashMap<String, byte[]>());
     private final C14NStack<XMLSecEvent> outputStack = new C14NStack<>();
     private boolean includeComments = false;
     private DocumentLevel currentDocumentLevel = DocumentLevel.NODE_BEFORE_DOCUMENT_ELEMENT;
@@ -285,11 +285,11 @@
                     outputStream.write('<');
                     final String prefix = xmlSecStartElement.getName().getPrefix();
                     if (prefix != null && !prefix.isEmpty()) {
-                        UtfHelpper.writeByte(prefix, outputStream, cache);
+                        UtfHelpper.writeByte(prefix, outputStream, CACHE);
                         outputStream.write(DOUBLEPOINT);
                     }
                     final String name = xmlSecStartElement.getName().getLocalPart();
-                    UtfHelpper.writeByte(name, outputStream, cache);
+                    UtfHelpper.writeByte(name, outputStream, CACHE);
 
                     if (!utilizedNamespaces.isEmpty()) {
                         Collections.sort(utilizedNamespaces);
@@ -300,9 +300,9 @@
                             }
 
                             if (xmlSecNamespace.isDefaultNamespaceDeclaration()) {
-                                outputAttrToWriter(null, XMLNS, xmlSecNamespace.getNamespaceURI(), outputStream, cache);
+                                outputAttrToWriter(null, XMLNS, xmlSecNamespace.getNamespaceURI(), outputStream, CACHE);
                             } else {
-                                outputAttrToWriter(XMLNS, xmlSecNamespace.getPrefix(), xmlSecNamespace.getNamespaceURI(), outputStream, cache);
+                                outputAttrToWriter(XMLNS, xmlSecNamespace.getPrefix(), xmlSecNamespace.getNamespaceURI(), outputStream, CACHE);
                             }
                         }
                     }
@@ -315,9 +315,9 @@
                             final QName attributeName = xmlSecAttribute.getName();
                             final String attributeNamePrefix = attributeName.getPrefix();
                             if (attributeNamePrefix != null && !attributeNamePrefix.isEmpty()) {
-                                outputAttrToWriter(attributeNamePrefix, attributeName.getLocalPart(), xmlSecAttribute.getValue(), outputStream, cache);
+                                outputAttrToWriter(attributeNamePrefix, attributeName.getLocalPart(), xmlSecAttribute.getValue(), outputStream, CACHE);
                             } else {
-                                outputAttrToWriter(null, attributeName.getLocalPart(), xmlSecAttribute.getValue(), outputStream, cache);
+                                outputAttrToWriter(null, attributeName.getLocalPart(), xmlSecAttribute.getValue(), outputStream, CACHE);
                             }
                         }
                     }
@@ -329,10 +329,10 @@
                     final String localPrefix = xmlSecEndElement.getName().getPrefix();
                     outputStream.write(_END_TAG);
                     if (localPrefix != null && !localPrefix.isEmpty()) {
-                        UtfHelpper.writeByte(localPrefix, outputStream, cache);
+                        UtfHelpper.writeByte(localPrefix, outputStream, CACHE);
                         outputStream.write(DOUBLEPOINT);
                     }
-                    UtfHelpper.writeByte(xmlSecEndElement.getName().getLocalPart(), outputStream, cache);
+                    UtfHelpper.writeByte(xmlSecEndElement.getName().getLocalPart(), outputStream, CACHE);
                     outputStream.write('>');
 
                     //We finished with this level, pop to the previous definitions.
@@ -416,13 +416,13 @@
     }
 
     protected static void outputAttrToWriter(final String prefix, final String name, final String value, final OutputStream writer,
-                                             final Map<String, byte[]> cache) throws IOException {
+                                             final Map<String, byte[]> CACHE) throws IOException {
         writer.write(' ');
         if (prefix != null) {
-            UtfHelpper.writeByte(prefix, writer, cache);
+            UtfHelpper.writeByte(prefix, writer, CACHE);
             UtfHelpper.writeCodePointToUtf8(DOUBLEPOINT, writer);
         }
-        UtfHelpper.writeByte(name, writer, cache);
+        UtfHelpper.writeByte(name, writer, CACHE);
         writer.write(EQUAL_STRING);
         byte[] toWrite;
         final int length = value.length();