What causes "Invalid system property: ${prop}" in quarkusio/quarkus?

Always supply a value: use foo= (empty value) instead of bare foo

quarkusio/quarkus · error · RuntimeException

Invalid system property: ${prop}

Error message

Invalid system property: ${prop}

What it means

RunMojo (mvn quarkus:dev) parses the comma-separated `jvmArgs`-style system property list and requires every entry to be in key=value form. When a split on '=' yields anything other than 2 parts (e.g. no '=' at all), it throws RuntimeException 'Invalid system property: <prop>'. The offending property name is interpolated into the message.

Source

Thrown at devtools/maven/src/main/java/io/quarkus/maven/RunMojo.java:128

                            break;
                        }
                    } else if (cmds.size() > 2) {
                        tooMany.set(cmds.keySet().stream().collect(Collectors.joining(" ")));
                        return;
                    } else {
                        throw new RuntimeException("Should never reach this!");
                    }
                    List<String> args = (List<String>) cmd.get(0);
                    if (additionalSystemProperties != null) {
                        String[] props = additionalSystemProperties.split(",");
                        for (int i = props.length - 1; i >= 0; i--) {
                            String prop = props[i];
                            String[] parts = prop.split("=");
                            if (parts.length == 2) {
                                // we want to set the system property write after the command
                                args.add(1, "-D" + prop);
                            } else {
                                throw new RuntimeException("Invalid system property: " + prop);
                            }
                        }
                    }
                    if (programArguments != null) {
                        args.addAll(Arrays.asList(programArguments.split(",")));
                    }
                    if (getLog().isInfoEnabled()) {
                        getLog().info("Executing \"" + String.join(" ", args) + "\"");
                    }
                    Path workingDirectory = (Path) cmd.get(1);
                    var pb = ProcessBuilder.newBuilder(args.get(0))
                            .arguments(args.subList(1, args.size()))
                            .output().inherited()
                            .error().inherited();
                    if (workingDirectory != null) {
                        pb.directory(workingDirectory);
                    }
                    if ((environmentVariables != null) && !environmentVariables.isEmpty()) {

View on GitHub (pinned to e1c734241f)

Solutions

Always supply a value: use foo= (empty value) instead of bare foo
For values containing '=', check the current Quarkus version: newer code splits with a limit; upgrade quarkus-maven-plugin, or quote/encode the value
Ensure the list is comma-separated with no stray spaces; trim entries
If you need a property set without a value, set it as -Dfoo= via the run arguments instead

Example fix

// before
-Dquarkus.jvm.args=-Dmy.prop
// after
-Dquarkus.jvm.args=-Dmy.prop=
// or for values containing '='
-Dquarkus.jvm.args="-Dmy.prop=foo==bar" (only on versions using split("=",2))

Defensive patterns

Strategy: validation

Validate before calling

// Validate each jvm/system property entry before invoking quarkus:dev:
for (String p : props.split(",")) {
  if (!p.matches("[^=]+=.*")) throw new IllegalArgumentException("Invalid system property: " + p);
}

Try / catch

try { runMojo.execute(); }
catch (RuntimeException e) {
  if (e.getMessage().startsWith("Invalid system property")) {
    log.error("Fix the jvmProps entry to key=value form: {}", e.getMessage());
  } else throw e;
}

Prevention

Always write properties as key=value, using key= for empty values
Avoid '=' inside property values unless your Quarkus version splits with limit 2
Don't put commas inside property values (the list is comma-separated)
Upgrade quarkus-maven-plugin to get tolerant value parsing

When it happens

Trigger: Passing a system property without a value or with malformed syntax to quarkus:dev, e.g. -Dquarkus.args.jvmProps (or the equivalent args entry) containing 'foo' or 'foo=bar=baz' style entries — split("=") on 'foo=bar=baz' yields 3 parts.

Common situations: Shorthand flags without values; copying -Dfoo from JVM command lines where the value was implicit; commas inside property values splitting the list; properties containing '=' in their value (e.g. base64) that produce >2 parts.

Related errors

AI-assisted analysis of quarkusio/quarkus@e1c734241f (2026-09-05). Data as JSON: /api/errors/5f5e10472dc792af. Report an issue: GitHub.