diff --git a/dd-java-agent/agent-bootstrap/src/main/java/datadog/trace/bootstrap/instrumentation/jdbc/JDBCConnectionUrlParser.java b/dd-java-agent/agent-bootstrap/src/main/java/datadog/trace/bootstrap/instrumentation/jdbc/JDBCConnectionUrlParser.java
index ce2c5bf77f4..2eaccd81400 100644
--- a/dd-java-agent/agent-bootstrap/src/main/java/datadog/trace/bootstrap/instrumentation/jdbc/JDBCConnectionUrlParser.java
+++ b/dd-java-agent/agent-bootstrap/src/main/java/datadog/trace/bootstrap/instrumentation/jdbc/JDBCConnectionUrlParser.java
@@ -81,13 +81,26 @@ DBInfo.Builder doParse(final String jdbcUrl, final DBInfo.Builder builder) {
       final String urlPart1;
       final String urlPart2;
       final int paramLoc;
+      char paramSeparator = ';';
 
       if (type.equals("db2") || type.equals("as400")) {
         if (jdbcUrl.contains("=")) {
           paramLoc = jdbcUrl.lastIndexOf(':');
-          urlPart1 = jdbcUrl.substring(0, paramLoc);
-          urlPart2 = jdbcUrl.substring(paramLoc + 1);
-
+          if (paramLoc > hostIndex + 2) {
+            urlPart1 = jdbcUrl.substring(0, paramLoc);
+            urlPart2 = jdbcUrl.substring(paramLoc + 1);
+          } else {
+            // No ':' past '://': fall back to '?' query-string params
+            final int queryLoc = jdbcUrl.indexOf('?');
+            if (queryLoc >= 0) {
+              urlPart1 = jdbcUrl.substring(0, queryLoc);
+              urlPart2 = jdbcUrl.substring(queryLoc + 1);
+              paramSeparator = '&';
+            } else {
+              urlPart1 = jdbcUrl;
+              urlPart2 = null;
+            }
+          }
         } else {
           urlPart1 = jdbcUrl;
           urlPart2 = null;
@@ -99,7 +112,7 @@ DBInfo.Builder doParse(final String jdbcUrl, final DBInfo.Builder builder) {
       }
 
       if (urlPart2 != null) {
-        final Map<String, String> props = splitQuery(urlPart2, ';');
+        final Map<String, String> props = splitQuery(urlPart2, paramSeparator);
         populateStandardProperties(builder, props);
         if (props.containsKey("servername")) {
           serverName = props.get("servername");
diff --git a/dd-java-agent/agent-bootstrap/src/test/java/datadog/trace/bootstrap/instrumentation/jdbc/JDBCConnectionUrlParserDB2Test.java b/dd-java-agent/agent-bootstrap/src/test/java/datadog/trace/bootstrap/instrumentation/jdbc/JDBCConnectionUrlParserDB2Test.java
new file mode 100644
index 00000000000..091c1e2b02f
--- /dev/null
+++ b/dd-java-agent/agent-bootstrap/src/test/java/datadog/trace/bootstrap/instrumentation/jdbc/JDBCConnectionUrlParserDB2Test.java
@@ -0,0 +1,35 @@
+package datadog.trace.bootstrap.instrumentation.jdbc;
+
+import static datadog.trace.bootstrap.instrumentation.jdbc.JDBCConnectionUrlParser.extractDBInfo;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import org.tabletest.junit.TableTest;
+
+/**
+ * Tests for DB2/AS400 JDBC URL parsing when the URL contains '=' but no explicit port.
+ *
+ * <p>Without a port, {@code lastIndexOf(':')} returns the scheme colon, making {@code urlPart1} too
+ * short for the subsequent {@code substring()} call and causing a {@code
+ * StringIndexOutOfBoundsException}.
+ */
+class JDBCConnectionUrlParserDB2Test {
+
+  @TableTest({
+    "scenario                             | url                                                        | type  | host     | instance | user    | db     ",
+    "DB2 with user param, no port         | jdbc:db2://db2.host/mydb?user=db2user                      | db2   | db2.host | mydb     | db2user | mydb   ",
+    "AS400 with user param, no port       | jdbc:as400://ashost/asdb?user=asuser                       | as400 | ashost   | asdb     | asuser  | asdb   ",
+    "DB2 with multiple params, no port    | jdbc:db2://db2.host/mydb?user=db2user&connectionTimeout=30 | db2   | db2.host | mydb     | db2user | mydb   ",
+    "DB2 with databasename param, no port | jdbc:db2://db2.host/mydb?user=db2user&databasename=otherdb | db2   | db2.host | mydb     | db2user | otherdb",
+    "DB2 with port and colon params       | jdbc:db2://db2.host:50000/mydb:user=db2user                | db2   | db2.host | mydb     | db2user | mydb   ",
+    "DB2 no params                        | jdbc:db2://db2.host/mydb                                   | db2   | db2.host | mydb     |         | mydb   "
+  })
+  void db2UrlWithEqualsAndNoPortShouldParseCorrectly(
+      String url, String type, String host, String instance, String user, String db) {
+    DBInfo info = extractDBInfo(url, null);
+    assertEquals(type, info.getType());
+    assertEquals(host, info.getHost());
+    assertEquals(instance, info.getInstance());
+    assertEquals(user, info.getUser());
+    assertEquals(db, info.getDb());
+  }
+}