diff --git a/implementation/src/main/java/io/smallrye/config/ConfigMappingContext.java b/implementation/src/main/java/io/smallrye/config/ConfigMappingContext.java
index cb4bf9ee9..906597950 100644
--- a/implementation/src/main/java/io/smallrye/config/ConfigMappingContext.java
+++ b/implementation/src/main/java/io/smallrye/config/ConfigMappingContext.java
@@ -323,7 +323,8 @@ public void accept(Function<String, Object> get) {
                             });
                         }
 
-                        Set<String> mapKeys = new HashSet<>();
+                        Map<String, String> mapKeys = new HashMap<>();
+                        Map<String, List<String>> mapProperties = new HashMap<>();
                         for (String propertyName : config.getPropertyNames()) {
                             if (propertyName.length() > path.length() + 1 // only consider properties bigger than the map path
                                     && (path.isEmpty() || propertyName.charAt(path.length()) == '.') // next char must be a dot (for the key)
@@ -337,29 +338,49 @@ public void accept(Function<String, Object> get) {
                                 mapProperty.next();
 
                                 String mapKey = unindexed(mapProperty.getPreviousSegment());
-                                // Nested property names use the same key for the same element, so track keys and skip if we already handled it
-                                if (mapKeys.contains(mapKey)) {
-                                    continue;
-                                }
-
-                                mapKeys.add(mapKey);
-                                String mapNext = unindexed(propertyName.substring(0, mapProperty.getPosition()));
+                                mapKeys.computeIfAbsent(mapKey, new Function<String, String>() {
+                                    @Override
+                                    public String apply(final String s) {
+                                        return unindexed(propertyName.substring(0, mapProperty.getPosition()));
+                                    }
+                                });
 
-                                nestedCreators.add(new Consumer<>() {
+                                mapProperties.computeIfAbsent(mapKey, new Function<String, List<String>>() {
                                     @Override
-                                    public void accept(Function<String, Object> get) {
-                                        // The properties may have been used ih the unnamed key, which cause clashes, so we skip them
-                                        if (unnamedKey != null && usedProperties.contains(propertyName)) {
+                                    public List<String> apply(final String s) {
+                                        return new ArrayList<>();
+                                    }
+                                });
+                                mapProperties.get(mapKey).add(propertyName);
+                            }
+                        }
+
+                        for (Map.Entry<String, String> mapKey : mapKeys.entrySet()) {
+                            nestedCreators.add(new Consumer<>() {
+                                @Override
+                                public void accept(Function<String, Object> get) {
+                                    // The properties may have been used ih the unnamed key, which cause clashes, so we skip them
+                                    if (unnamedKey != null) {
+                                        boolean allUsed = true;
+                                        for (String mapProperty : mapProperties.get(mapKey.getKey())) {
+                                            if (!usedProperties.contains(mapProperty)) {
+                                                allUsed = false;
+                                                break;
+                                            }
+                                        }
+                                        if (allUsed) {
                                             return;
                                         }
+                                    }
 
-                                        V value = (V) get.apply(mapNext);
-                                        if (value != null) {
-                                            map.put(keyConverter.convert(mapKey), value);
-                                        }
+                                    // This is the full path plus the map key
+                                    V value = (V) get.apply(mapKey.getValue());
+                                    if (value != null) {
+                                        map.put(keyConverter.convert(mapKey.getKey()), value);
                                     }
-                                });
-                            }
+                                }
+                            });
+
                         }
 
                         return map;
diff --git a/implementation/src/test/java/io/smallrye/config/ConfigMappingFullTest.java b/implementation/src/test/java/io/smallrye/config/ConfigMappingFullTest.java
new file mode 100644
index 000000000..b31ff9f23
--- /dev/null
+++ b/implementation/src/test/java/io/smallrye/config/ConfigMappingFullTest.java
@@ -0,0 +1,239 @@
+package io.smallrye.config;
+
+import static io.smallrye.config.KeyValuesConfigSource.config;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import java.util.Map;
+import java.util.Optional;
+import java.util.OptionalInt;
+
+import org.junit.jupiter.api.Test;
+
+public class ConfigMappingFullTest {
+    @Test
+    void ambiguousUnnamedKeysDefaults() {
+        SmallRyeConfig config = new SmallRyeConfigBuilder()
+                .withSources(config(
+                        "datasource.postgresql.jdbc.url", "value",
+                        "datasource.postgresql.password", "value"))
+                .withMapping(DataSourcesJdbcRuntimeConfig.class)
+                .withMapping(DataSourcesJdbcBuildTimeConfig.class)
+                .withMapping(DataSourcesRuntimeConfig.class)
+                .withMapping(DataSourcesBuildTimeConfig.class)
+                .build();
+
+        assertTrue(
+                config.getConfigMapping(DataSourcesRuntimeConfig.class).dataSources().get("postgresql").password().isPresent());
+
+        config = new SmallRyeConfigBuilder()
+                .withSources(config(
+                        "datasource.postgresql.jdbc.url", "value",
+                        "datasource.postgresql.password", "value"))
+                .withMapping(DataSourcesJdbcBuildTimeConfig.class)
+                .withMapping(DataSourcesJdbcRuntimeConfig.class)
+                .withMapping(DataSourcesRuntimeConfig.class)
+                .withMapping(DataSourcesBuildTimeConfig.class)
+                .build();
+
+        assertTrue(
+                config.getConfigMapping(DataSourcesRuntimeConfig.class).dataSources().get("postgresql").password().isPresent());
+
+        config = new SmallRyeConfigBuilder()
+                .withSources(config(
+                        "datasource.postgresql.jdbc.url", "value",
+                        "datasource.postgresql.password", "value"))
+                .withMapping(DataSourcesJdbcBuildTimeConfig.class)
+                .withMapping(DataSourcesJdbcRuntimeConfig.class)
+                .withMapping(DataSourcesBuildTimeConfig.class)
+                .withMapping(DataSourcesRuntimeConfig.class)
+                .build();
+
+        assertTrue(
+                config.getConfigMapping(DataSourcesRuntimeConfig.class).dataSources().get("postgresql").password().isPresent());
+
+        config = new SmallRyeConfigBuilder()
+                .withSources(config(
+                        "datasource.postgresql.jdbc.url", "value",
+                        "datasource.postgresql.password", "value"))
+                .withMapping(DataSourcesRuntimeConfig.class)
+                .withMapping(DataSourcesJdbcBuildTimeConfig.class)
+                .withMapping(DataSourcesJdbcRuntimeConfig.class)
+                .withMapping(DataSourcesBuildTimeConfig.class)
+                .build();
+
+        assertTrue(
+                config.getConfigMapping(DataSourcesRuntimeConfig.class).dataSources().get("postgresql").password().isPresent());
+    }
+
+    @ConfigMapping(prefix = "datasource")
+    interface DataSourcesRuntimeConfig {
+        @WithParentName
+        @WithDefaults
+        @WithUnnamedKey("<default>")
+        Map<String, DataSourceRuntimeConfig> dataSources();
+
+        interface DataSourceRuntimeConfig {
+            @WithDefault("true")
+            boolean active();
+
+            Optional<String> username();
+
+            Optional<String> password();
+
+            Optional<String> credentialsProvider();
+
+            Optional<String> credentialsProviderName();
+        }
+    }
+
+    @ConfigMapping(prefix = "datasource")
+    interface DataSourcesJdbcRuntimeConfig {
+        DataSourceJdbcRuntimeConfig jdbc();
+
+        @WithParentName
+        @WithDefaults
+        Map<String, DataSourceJdbcOuterNamedRuntimeConfig> namedDataSources();
+
+        interface DataSourceJdbcOuterNamedRuntimeConfig {
+            DataSourceJdbcRuntimeConfig jdbc();
+        }
+
+        interface DataSourceJdbcRuntimeConfig {
+            Optional<String> url();
+
+            OptionalInt initialSize();
+
+            @WithDefault("0")
+            int minSize();
+
+            @WithDefault("20")
+            int maxSize();
+
+            @WithDefault("2M")
+            String backgroundValidationInterval();
+
+            Optional<String> foregroundValidationInterval();
+
+            @WithDefault("5S")
+            Optional<String> acquisitionTimeout();
+
+            Optional<String> leakDetectionInterval();
+
+            @WithDefault("5M")
+            String idleRemovalInterval();
+
+            Optional<String> maxLifetime();
+
+            @WithDefault("false")
+            boolean extendedLeakReport();
+
+            @WithDefault("false")
+            boolean flushOnClose();
+
+            @WithDefault("true")
+            boolean detectStatementLeaks();
+
+            Optional<String> newConnectionSql();
+
+            Optional<String> validationQuerySql();
+
+            @WithDefault("true")
+            boolean poolingEnabled();
+
+            Map<String, String> additionalJdbcProperties();
+
+            @WithName("telemetry.enabled")
+            Optional<Boolean> telemetry();
+        }
+    }
+
+    @ConfigMapping(prefix = "datasource")
+    interface DataSourcesBuildTimeConfig {
+        @WithParentName
+        @WithDefaults
+        @WithUnnamedKey("<default>")
+        Map<String, DataSourceBuildTimeConfig> dataSources();
+
+        @WithName("health.enabled")
+        @WithDefault("true")
+        boolean healthEnabled();
+
+        @WithName("metrics.enabled")
+        @WithDefault("false")
+        boolean metricsEnabled();
+
+        @Deprecated
+        Optional<String> url();
+
+        @Deprecated
+        Optional<String> driver();
+
+        interface DataSourceBuildTimeConfig {
+            Optional<String> dbKind();
+
+            Optional<String> dbVersion();
+
+            DevServicesBuildTimeConfig devservices();
+
+            @WithDefault("false")
+            boolean healthExclude();
+
+            interface DevServicesBuildTimeConfig {
+                Optional<Boolean> enabled();
+
+                Optional<String> imageName();
+
+                Map<String, String> containerEnv();
+
+                Map<String, String> containerProperties();
+
+                Map<String, String> properties();
+
+                OptionalInt port();
+
+                Optional<String> command();
+
+                Optional<String> dbName();
+
+                Optional<String> username();
+
+                Optional<String> password();
+
+                Optional<String> initScriptPath();
+
+                Map<String, String> volumes();
+
+                @WithDefault("true")
+                boolean reuse();
+            }
+        }
+    }
+
+    @ConfigMapping(prefix = "datasource")
+    interface DataSourcesJdbcBuildTimeConfig {
+        @WithParentName
+        @WithDefaults
+        @WithUnnamedKey("<ddefault>")
+        Map<String, DataSourceJdbcOuterNamedBuildTimeConfig> dataSources();
+
+        interface DataSourceJdbcOuterNamedBuildTimeConfig {
+            DataSourceJdbcBuildTimeConfig jdbc();
+
+            interface DataSourceJdbcBuildTimeConfig {
+                @WithParentName
+                @WithDefault("true")
+                boolean enabled();
+
+                Optional<String> driver();
+
+                Optional<Boolean> enableMetrics();
+
+                @WithDefault("false")
+                boolean tracing();
+
+                @WithDefault("false")
+                boolean telemetry();
+            }
+        }
+    }
+}