diff --git a/org.hl7.fhir.convertors/src/test/java/org/hl7/fhir/convertors/conv40_50/AuditEvent40_50Test.java b/org.hl7.fhir.convertors/src/test/java/org/hl7/fhir/convertors/conv40_50/AuditEvent40_50Test.java
new file mode 100644
index 000000000..244768be4
--- /dev/null
+++ b/org.hl7.fhir.convertors/src/test/java/org/hl7/fhir/convertors/conv40_50/AuditEvent40_50Test.java
@@ -0,0 +1,91 @@
+package org.hl7.fhir.convertors.conv40_50;
+
+import org.apache.commons.codec.binary.Base64;
+import org.hl7.fhir.convertors.factory.VersionConvertorFactory_40_50;
+import org.junit.jupiter.api.DisplayName;
+import org.junit.jupiter.api.Test;
+
+import java.io.ByteArrayInputStream;
+import java.io.ByteArrayOutputStream;
+import java.io.IOException;
+import java.io.InputStream;
+
+import static org.junit.jupiter.api.Assertions.assertArrayEquals;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+public class AuditEvent40_50Test {
+
+  public static final String THE_BASE_64_BINARY_STRING = "dGhpcyBpcyB2YWxpZCBiYXNlNjQ=";
+  public static final byte[] THE_BASE_64_BINARY_BYTE_ARRAY = Base64.decodeBase64(THE_BASE_64_BINARY_STRING.getBytes(ca.uhn.fhir.rest.api.Constants.CHARSET_UTF8));
+
+  public static final String INVALID_BASE_64_BINARY_STRING = "Picard was the best starship captain";
+  public static final byte[] INVALID_BASE_64_BINARY_BYTE_ARRAY = Base64.decodeBase64(THE_BASE_64_BINARY_STRING.getBytes(ca.uhn.fhir.rest.api.Constants.CHARSET_UTF8));
+
+
+  @Test
+  @DisplayName("Test r5 -> r4 AuditEvent conversion.")
+  public void testR5_R4() throws IOException {
+    InputStream r5_input = this.getClass().getResourceAsStream("/auditevent_50_with_base64binary.json");
+
+    org.hl7.fhir.r5.model.AuditEvent r5_actual = (org.hl7.fhir.r5.model.AuditEvent) new org.hl7.fhir.r5.formats.JsonParser().parse(r5_input);
+    org.hl7.fhir.r4.model.Resource r4_conv = VersionConvertorFactory_40_50.convertResource(r5_actual);
+
+    org.hl7.fhir.r4.formats.JsonParser r4_parser = new org.hl7.fhir.r4.formats.JsonParser();
+
+    ByteArrayOutputStream stream = new ByteArrayOutputStream();
+    r4_parser.compose(stream, r4_conv);
+
+    org.hl7.fhir.r4.model.Resource r4_streamed = (org.hl7.fhir.r4.model.AuditEvent) new org.hl7.fhir.r4.formats.JsonParser().parse(new ByteArrayInputStream(stream.toByteArray()));
+
+    assertArrayEquals(((org.hl7.fhir.r4.model.AuditEvent)r4_conv).getEntity().get(0).getQuery(), THE_BASE_64_BINARY_BYTE_ARRAY);
+    assertArrayEquals(((org.hl7.fhir.r4.model.AuditEvent)r4_streamed).getEntity().get(0).getQuery(), THE_BASE_64_BINARY_BYTE_ARRAY);
+  }
+
+  @Test
+  @DisplayName("Test r5 -> r4 AuditEvent conversion.")
+  public void testR4_R5() throws IOException {
+    InputStream r4_input = this.getClass().getResourceAsStream("/auditevent_40_with_base64binary.json");
+
+    org.hl7.fhir.r4.model.AuditEvent r4_actual = (org.hl7.fhir.r4.model.AuditEvent) new org.hl7.fhir.r4.formats.JsonParser().parse(r4_input);
+    org.hl7.fhir.r5.model.Resource r5_conv = VersionConvertorFactory_40_50.convertResource(r4_actual);
+
+    org.hl7.fhir.r5.formats.JsonParser r5_parser = new org.hl7.fhir.r5.formats.JsonParser();
+
+    ByteArrayOutputStream stream
+      = new ByteArrayOutputStream();
+
+    r5_parser.compose(stream, r5_conv);
+
+    org.hl7.fhir.r5.model.Resource r5_streamed = (org.hl7.fhir.r5.model.AuditEvent) new org.hl7.fhir.r5.formats.JsonParser().parse(new ByteArrayInputStream(stream.toByteArray()));
+
+    assertArrayEquals(((org.hl7.fhir.r5.model.AuditEvent)r5_conv).getEntity().get(0).getQuery(), THE_BASE_64_BINARY_BYTE_ARRAY);
+    assertArrayEquals(((org.hl7.fhir.r5.model.AuditEvent)r5_streamed).getEntity().get(0).getQuery(), THE_BASE_64_BINARY_BYTE_ARRAY);
+
+  }
+
+  @Test
+  @DisplayName("Test r5 -> r4 AuditEvent conversion with invalid Base64Binary.")
+  public void testR4_R5BadBase64Binary() throws IOException {
+    InputStream r4_input = this.getClass().getResourceAsStream("/auditevent_40_with_invalid_base64binary.json");
+
+    org.hl7.fhir.r4.model.AuditEvent r4_actual = (org.hl7.fhir.r4.model.AuditEvent) new org.hl7.fhir.r4.formats.JsonParser().parse(r4_input);
+
+    org.hl7.fhir.r5.model.Resource r5_conv = VersionConvertorFactory_40_50.convertResource(r4_actual);
+
+    org.hl7.fhir.r5.formats.JsonParser r5_parser = new org.hl7.fhir.r5.formats.JsonParser();
+
+    ByteArrayOutputStream stream
+      = new ByteArrayOutputStream();
+
+    r5_parser.compose(stream, r5_conv);
+
+    org.hl7.fhir.r5.model.Resource r5_streamed = (org.hl7.fhir.r5.model.AuditEvent) new org.hl7.fhir.r5.formats.JsonParser().parse(new ByteArrayInputStream(stream.toByteArray()));
+
+    System.out.println(((org.hl7.fhir.r5.model.AuditEvent)r5_conv).getEntity().get(0).getQueryElement().getValueAsString());
+
+    //FIXME we should not be even getting this far.
+    assertArrayEquals(((org.hl7.fhir.r5.model.AuditEvent)r5_conv).getEntity().get(0).getQuery(), INVALID_BASE_64_BINARY_BYTE_ARRAY);
+    assertArrayEquals(((org.hl7.fhir.r5.model.AuditEvent)r5_streamed).getEntity().get(0).getQuery(), INVALID_BASE_64_BINARY_BYTE_ARRAY);
+
+  }
+}
diff --git a/org.hl7.fhir.convertors/src/test/resources/auditevent_40_with_base64binary.json b/org.hl7.fhir.convertors/src/test/resources/auditevent_40_with_base64binary.json
new file mode 100644
index 000000000..ed6c0ff6d
--- /dev/null
+++ b/org.hl7.fhir.convertors/src/test/resources/auditevent_40_with_base64binary.json
@@ -0,0 +1,122 @@
+{
+  "resourceType": "AuditEvent",
+  "id": "example",
+  "text": {
+    "status": "generated",
+    "div": "<div xmlns=\"http://www.w3.org/1999/xhtml\">Application Start for under service login &quot;Grahame&quot; (id: Grahame's Test HL7Connect)</div>"
+  },
+  "type": {
+    "system": "http://dicom.nema.org/resources/ontology/DCM",
+    "code": "110100",
+    "display": "Application Activity"
+  },
+  "subtype": [
+    {
+      "system": "http://dicom.nema.org/resources/ontology/DCM",
+      "code": "110120",
+      "display": "Application Start"
+    }
+  ],
+  "action": "E",
+  "recorded": "2012-10-25T22:04:27+11:00",
+  "outcome": "0",
+  "agent": [
+    {
+      "type": {
+        "coding": [
+          {
+            "system": "http://terminology.hl7.org/CodeSystem/extra-security-role-type",
+            "code": "humanuser",
+            "display": "human user"
+          }
+        ]
+      },
+      "role": [
+        {
+          "text": "Service User (Logon)"
+        }
+      ],
+      "who": {
+        "identifier": {
+          "value": "Grahame"
+        }
+      },
+      "requestor": false,
+      "network": {
+        "address": "127.0.0.1",
+        "type": "2"
+      }
+    },
+    {
+      "type": {
+        "coding": [
+          {
+            "system": "http://dicom.nema.org/resources/ontology/DCM",
+            "code": "110153",
+            "display": "Source Role ID"
+          }
+        ]
+      },
+      "who": {
+        "identifier": {
+          "system": "urn:oid:2.16.840.1.113883.4.2",
+          "value": "2.16.840.1.113883.4.2"
+        }
+      },
+      "altId": "6580",
+      "requestor": false,
+      "network": {
+        "address": "Workstation1.ehr.familyclinic.com",
+        "type": "1"
+      }
+    }
+  ],
+  "source": {
+    "site": "Development",
+    "observer": {
+      "display": "Grahame's Laptop"
+    },
+    "type": [
+      {
+        "system": "http://dicom.nema.org/resources/ontology/DCM",
+        "code": "110122",
+        "display": "Login"
+      }
+    ]
+  },
+  "entity": [
+    {
+      "what": {
+        "identifier": {
+          "type": {
+            "coding": [
+              {
+                "system": "http://terminology.hl7.org/CodeSystem/v2-0203",
+                "code": "SNO"
+              }
+            ],
+            "text": "Dell Serial Number"
+          },
+          "value": "ABCDEF"
+        }
+      },
+      "type": {
+        "system": "http://terminology.hl7.org/CodeSystem/audit-entity-type",
+        "code": "4",
+        "display": "Other"
+      },
+      "role": {
+        "system": "http://terminology.hl7.org/CodeSystem/object-role",
+        "code": "4",
+        "display": "Domain Resource"
+      },
+      "lifecycle": {
+        "system": "http://terminology.hl7.org/CodeSystem/dicom-audit-lifecycle",
+        "code": "6",
+        "display": "Access / Use"
+      },
+      "name": "Grahame's Laptop",
+      "query" : "dGhpcyBpcyB2YWxpZCBiYXNlNjQ="
+    }
+  ]
+}
\ No newline at end of file
diff --git a/org.hl7.fhir.convertors/src/test/resources/auditevent_40_with_invalid_base64binary.json b/org.hl7.fhir.convertors/src/test/resources/auditevent_40_with_invalid_base64binary.json
new file mode 100644
index 000000000..146cb7520
--- /dev/null
+++ b/org.hl7.fhir.convertors/src/test/resources/auditevent_40_with_invalid_base64binary.json
@@ -0,0 +1,122 @@
+{
+  "resourceType": "AuditEvent",
+  "id": "example",
+  "text": {
+    "status": "generated",
+    "div": "<div xmlns=\"http://www.w3.org/1999/xhtml\">Application Start for under service login &quot;Grahame&quot; (id: Grahame's Test HL7Connect)</div>"
+  },
+  "type": {
+    "system": "http://dicom.nema.org/resources/ontology/DCM",
+    "code": "110100",
+    "display": "Application Activity"
+  },
+  "subtype": [
+    {
+      "system": "http://dicom.nema.org/resources/ontology/DCM",
+      "code": "110120",
+      "display": "Application Start"
+    }
+  ],
+  "action": "E",
+  "recorded": "2012-10-25T22:04:27+11:00",
+  "outcome": "0",
+  "agent": [
+    {
+      "type": {
+        "coding": [
+          {
+            "system": "http://terminology.hl7.org/CodeSystem/extra-security-role-type",
+            "code": "humanuser",
+            "display": "human user"
+          }
+        ]
+      },
+      "role": [
+        {
+          "text": "Service User (Logon)"
+        }
+      ],
+      "who": {
+        "identifier": {
+          "value": "Grahame"
+        }
+      },
+      "requestor": false,
+      "network": {
+        "address": "127.0.0.1",
+        "type": "2"
+      }
+    },
+    {
+      "type": {
+        "coding": [
+          {
+            "system": "http://dicom.nema.org/resources/ontology/DCM",
+            "code": "110153",
+            "display": "Source Role ID"
+          }
+        ]
+      },
+      "who": {
+        "identifier": {
+          "system": "urn:oid:2.16.840.1.113883.4.2",
+          "value": "2.16.840.1.113883.4.2"
+        }
+      },
+      "altId": "6580",
+      "requestor": false,
+      "network": {
+        "address": "Workstation1.ehr.familyclinic.com",
+        "type": "1"
+      }
+    }
+  ],
+  "source": {
+    "site": "Development",
+    "observer": {
+      "display": "Grahame's Laptop"
+    },
+    "type": [
+      {
+        "system": "http://dicom.nema.org/resources/ontology/DCM",
+        "code": "110122",
+        "display": "Login"
+      }
+    ]
+  },
+  "entity": [
+    {
+      "what": {
+        "identifier": {
+          "type": {
+            "coding": [
+              {
+                "system": "http://terminology.hl7.org/CodeSystem/v2-0203",
+                "code": "SNO"
+              }
+            ],
+            "text": "Dell Serial Number"
+          },
+          "value": "ABCDEF"
+        }
+      },
+      "type": {
+        "system": "http://terminology.hl7.org/CodeSystem/audit-entity-type",
+        "code": "4",
+        "display": "Other"
+      },
+      "role": {
+        "system": "http://terminology.hl7.org/CodeSystem/object-role",
+        "code": "4",
+        "display": "Domain Resource"
+      },
+      "lifecycle": {
+        "system": "http://terminology.hl7.org/CodeSystem/dicom-audit-lifecycle",
+        "code": "6",
+        "display": "Access / Use"
+      },
+      "name": "Grahame's Laptop",
+      "query" : "Picard was the best starship captain"
+    }
+  ]
+}
\ No newline at end of file
diff --git a/org.hl7.fhir.convertors/src/test/resources/auditevent_50_with_base64binary.json b/org.hl7.fhir.convertors/src/test/resources/auditevent_50_with_base64binary.json
new file mode 100644
index 000000000..5bd96899f
--- /dev/null
+++ b/org.hl7.fhir.convertors/src/test/resources/auditevent_50_with_base64binary.json
@@ -0,0 +1,117 @@
+{
+  "resourceType": "AuditEvent",
+  "id": "example",
+  "text": {
+    "status": "generated",
+    "div": "<div xmlns=\"http://www.w3.org/1999/xhtml\">Application Start for under service login &quot;Grahame&quot; (id: Grahame's Test HL7Connect)</div>"
+  },
+  "category": [
+    {
+      "coding": [
+        {
+          "system": "http://dicom.nema.org/resources/ontology/DCM",
+          "code": "110100",
+          "display": "Application Activity"
+        }
+      ]
+    }
+  ],
+  "code": {
+    "coding": [
+      {
+        "system": "http://dicom.nema.org/resources/ontology/DCM",
+        "code": "110120",
+        "display": "Application Start"
+      }
+    ]
+  },
+  "action": "E",
+  "recorded": "2012-10-25T22:04:27+11:00",
+  "outcome": {
+    "code": {
+      "system": "http://terminology.hl7.org/CodeSystem/audit-event-outcome",
+      "code": "0",
+      "display": "Success"
+    }
+  },
+  "agent": [
+    {
+      "role": [
+        {
+          "text": "Service User (Logon)"
+        }
+      ],
+      "who": {
+        "identifier": {
+          "value": "Grahame"
+        }
+      },
+      "requestor": false
+    },
+    {
+      "extension": [
+        {
+          "url": "http://hl7.org/fhir/StructureDefinition/auditevent-AlternativeUserID",
+          "valueIdentifier": {
+            "type": {
+              "text": "process ID"
+            },
+            "value": "6580"
+          }
+        }
+      ],
+      "who": {
+        "identifier": {
+          "system": "urn:oid:2.16.840.1.113883.4.2",
+          "value": "2.16.840.1.113883.4.2"
+        }
+      },
+      "requestor": false,
+      "networkString": "Workstation1.ehr.familyclinic.com"
+    }
+  ],
+  "source": {
+    "observer": {
+      "display": "Grahame's Laptop"
+    },
+    "type": [
+      {
+        "coding": [
+          {
+            "system": "http://dicom.nema.org/resources/ontology/DCM",
+            "code": "110122",
+            "display": "Login"
+          }
+        ]
+      }
+    ]
+  },
+  "entity": [
+    {
+      "what": {
+        "identifier": {
+          "type": {
+            "coding": [
+              {
+                "system": "http://terminology.hl7.org/CodeSystem/v2-0203",
+                "code": "SNO"
+              }
+            ],
+            "text": "Dell Serial Number"
+          },
+          "value": "ABCDEF"
+        }
+      },
+      "role": {
+        "coding": [
+          {
+            "system": "http://terminology.hl7.org/CodeSystem/object-role",
+            "code": "4",
+            "display": "Domain Resource"
+          }
+        ]
+      },
+      "query" : "dGhpcyBpcyB2YWxpZCBiYXNlNjQ="
+    }
+  ]
+}
\ No newline at end of file