diff --git a/extensions/resteasy-classic/resteasy-common/runtime/src/main/java/io/quarkus/resteasy/common/runtime/config/ThresholdConverter.java b/extensions/resteasy-classic/resteasy-common/runtime/src/main/java/io/quarkus/resteasy/common/runtime/config/ThresholdConverter.java
new file mode 100644
index 0000000000000..3744afff1cf19
--- /dev/null
+++ b/extensions/resteasy-classic/resteasy-common/runtime/src/main/java/io/quarkus/resteasy/common/runtime/config/ThresholdConverter.java
@@ -0,0 +1,70 @@
+package io.quarkus.resteasy.common.runtime.config;
+
+import static io.quarkus.runtime.configuration.ConverterSupport.DEFAULT_QUARKUS_CONVERTER_PRIORITY;
+
+import java.io.Serializable;
+import java.time.Duration;
+import java.util.Locale;
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
+
+import jakarta.annotation.Priority;
+
+import org.eclipse.microprofile.config.spi.Converter;
+import org.jboss.resteasy.spi.config.SizeUnit;
+import org.jboss.resteasy.spi.config.Threshold;
+
+/**
+ * A converter for a {@link Threshold} interface.
+ */
+@Priority(DEFAULT_QUARKUS_CONVERTER_PRIORITY)
+public class ThresholdConverter implements Converter<Threshold>, Serializable {
+
+    public static final Threshold NONE = Threshold.of(-1L, SizeUnit.BYTE);
+    public static final Threshold DEFAULT = Threshold.of(512L, SizeUnit.KILOBYTE);
+    private static final Pattern PATTERN = Pattern.compile("(?<size>-?(?!0)\\d+)\\s*(?<unit>(?:ZB|EB|TB|PB|GB|MB|KB|B)\\b)?");
+
+    public ThresholdConverter() {
+    }
+
+    /**
+     * The converter accepts a value which start with a number by implicitly appending `PT` to it.
+     * If the value consists only of a number, it implicitly treats the value as seconds.
+     * Otherwise, tries to convert the value assuming that it is in the accepted ISO-8601 duration format.
+     *
+     * @param value duration as String
+     * @return {@link Duration}
+     */
+    @Override
+    public Threshold convert(String value) {
+        value = value.trim();
+        if (value.isEmpty()) {
+            return null;
+        }
+
+        // The value should be something like 1 MB or 1MB
+        final Matcher matcher = PATTERN.matcher(value.toUpperCase(Locale.ROOT));
+        if (!matcher.find()) {
+            return DEFAULT;
+        }
+        final String stringSize = matcher.group("size");
+        final String stringUnit = matcher.group("unit");
+        final long size;
+        if (stringSize == null || stringSize.isBlank()) {
+            return DEFAULT;
+        } else {
+            size = Long.parseLong(stringSize);
+        }
+        if (size < 0L) {
+            return NONE;
+        }
+        SizeUnit unit = null;
+        for (SizeUnit u : SizeUnit.values()) {
+            if (u.abbreviation().equals(stringUnit)) {
+                unit = u;
+                break;
+            }
+        }
+        return Threshold.of(size, unit == null ? SizeUnit.BYTE : unit);
+    }
+}
diff --git a/extensions/resteasy-classic/resteasy-common/runtime/src/main/resources/META-INF/services/org.eclipse.microprofile.config.spi.Converter b/extensions/resteasy-classic/resteasy-common/runtime/src/main/resources/META-INF/services/org.eclipse.microprofile.config.spi.Converter
new file mode 100644
index 0000000000000..efa644813dcda
--- /dev/null
+++ b/extensions/resteasy-classic/resteasy-common/runtime/src/main/resources/META-INF/services/org.eclipse.microprofile.config.spi.Converter
@@ -0,0 +1 @@
+io.quarkus.resteasy.common.runtime.config.ThresholdConverter
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