diff --git a/spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/convert/QueryMapper.java b/spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/convert/QueryMapper.java
index a360b8be9..1013628de 100644
--- a/spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/convert/QueryMapper.java
+++ b/spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/convert/QueryMapper.java
@@ -1411,6 +1411,14 @@ public class QueryMapper {
 				this.currentIndex = 0;
 			}
 
+			String nextToken() {
+				return pathParts.get(currentIndex+1);
+			}
+
+			boolean hasNexToken() {
+				return pathParts.size() > currentIndex+1;
+			}
+
 			/**
 			 * Maps the property name while retaining potential positional operator {@literal $}.
 			 *
@@ -1420,31 +1428,25 @@ public class QueryMapper {
 			protected String mapPropertyName(MongoPersistentProperty property) {
 
 				StringBuilder mappedName = new StringBuilder(PropertyToFieldNameConverter.INSTANCE.convert(property));
-
-				boolean inspect = iterator.hasNext();
-
-				while (inspect) {
-
-					String partial = iterator.next();
-					currentIndex++;
-
-					boolean isPositional = isPositionalParameter(partial) && property.isCollectionLike();
-					if (property.isMap() && currentPropertyRoot.equals(partial) && iterator.hasNext()) {
-						partial = iterator.next();
-						currentIndex++;
-					}
-
-					if (isPositional || property.isMap() && !currentPropertyRoot.equals(partial)) {
-						mappedName.append(".").append(partial);
-					}
-
-					inspect = isPositional && iterator.hasNext();
+				if(!hasNexToken()) {
+					return mappedName.toString();
 				}
 
-				if (currentIndex + 1 < pathParts.size()) {
-					currentIndex++;
-					currentPropertyRoot = pathParts.get(currentIndex);
+				String nextToken = nextToken();
+				if(isPositionalParameter(nextToken)) {
+
+					mappedName.append(".").append(nextToken);
+					currentIndex+=2;
+					return mappedName.toString();
 				}
+
+				if(property.isMap()) {
+
+					mappedName.append(".").append(nextToken);
+					currentIndex+=2;
+					return mappedName.toString();
+				}
+				currentIndex++;
 				return mappedName.toString();
 			}
 
diff --git a/spring-data-mongodb/src/test/java/org/springframework/data/mongodb/core/convert/UpdateMapperUnitTests.java b/spring-data-mongodb/src/test/java/org/springframework/data/mongodb/core/convert/UpdateMapperUnitTests.java
index 15704af03..28d522fba 100644
--- a/spring-data-mongodb/src/test/java/org/springframework/data/mongodb/core/convert/UpdateMapperUnitTests.java
+++ b/spring-data-mongodb/src/test/java/org/springframework/data/mongodb/core/convert/UpdateMapperUnitTests.java
@@ -1309,6 +1309,36 @@ class UpdateMapperUnitTests {
 		assertThat(mappedUpdate).isEqualTo(new org.bson.Document("$set",new org.bson.Document("customers", Arrays.asList("c-name"))));
 	}
 
+	@Test // GH-3921
+	void mapNumericKeyInPathHavingComplexMapValyeTypes() {
+
+		Update update = new Update().set("testInnerData.testMap.1.intValue", "4");
+		Document mappedUpdate = mapper.getMappedObject(update.getUpdateObject(),
+				context.getPersistentEntity(TestData.class));
+
+		assertThat(mappedUpdate).isEqualTo(new org.bson.Document("$set",new org.bson.Document("testInnerData.testMap.1.intValue","4")));
+	}
+
+	@Test // GH-3921
+	void mapNumericKeyInPathNotMatchingExistingProperties() {
+
+		Update update = new Update().set("testInnerData.imaginaryMap.1.nonExistingProperty", "4");
+		Document mappedUpdate = mapper.getMappedObject(update.getUpdateObject(),
+				context.getPersistentEntity(TestData.class));
+
+		assertThat(mappedUpdate).isEqualTo(new org.bson.Document("$set",new org.bson.Document("testInnerData.imaginaryMap.1.noExistingProperty","4")));
+	}
+
+	@Test // GH-3921
+	void mapNumericKeyInPathPartiallyMatchingExistingProperties() {
+
+		Update update = new Update().set("testInnerData.testMap.1.nonExistingProperty.2.someValue", "4");
+		Document mappedUpdate = mapper.getMappedObject(update.getUpdateObject(),
+				context.getPersistentEntity(TestData.class));
+
+		assertThat(mappedUpdate).isEqualTo(new org.bson.Document("$set",new org.bson.Document("testInnerData.testMap.1.nonExistingProperty.2.someValue","4")));
+	}
+
 	static class DomainTypeWrappingConcreteyTypeHavingListOfInterfaceTypeAttributes {
 		ListModelWrapper concreteTypeWithListAttributeOfInterfaceType;
 	}
@@ -1710,4 +1740,20 @@ class UpdateMapperUnitTests {
 		private List<Sample> samples;
 	}
 
+	@Data
+	private static class TestData {
+		@Id
+		private String id;
+		private TestInnerData testInnerData;
+	}
+
+	@Data
+	private static class TestInnerData {
+		private Map<Integer, TestValue> testMap;
+	}
+
+	@Data
+	private static class TestValue {
+		private int intValue;
+	}
 }