diff --git a/projects/ngqp-demo/src/app/home/home.component.ts b/projects/ngqp-demo/src/app/home/home.component.ts
index 43aed8e..82ccef9 100644
--- a/projects/ngqp-demo/src/app/home/home.component.ts
+++ b/projects/ngqp-demo/src/app/home/home.component.ts
@@ -1,5 +1,5 @@
 import { Component } from '@angular/core';
-import { createStringDeserializer, QueryParamBuilder, QueryParamGroup } from '@ngqp/core';
+import { QueryParamBuilder, QueryParamGroup } from '@ngqp/core';
 import { faAlignLeft, faCogs, faGlassCheers, faHeart, IconDefinition } from '@fortawesome/free-solid-svg-icons';
 import { faGithub } from '@fortawesome/free-brands-svg-icons';
 
diff --git a/projects/ngqp/core/src/lib/directives/query-param-group.service.ts b/projects/ngqp/core/src/lib/directives/query-param-group.service.ts
index c512343..ffe959a 100644
--- a/projects/ngqp/core/src/lib/directives/query-param-group.service.ts
+++ b/projects/ngqp/core/src/lib/directives/query-param-group.service.ts
@@ -1,6 +1,6 @@
 import { Inject, Injectable, isDevMode, OnDestroy, Optional } from '@angular/core';
 import { Params } from '@angular/router';
-import { EMPTY, from, Observable, Subject, zip } from 'rxjs';
+import { EMPTY, forkJoin, from, Observable, Subject, zip } from 'rxjs';
 import {
     catchError,
     concatMap,
@@ -15,7 +15,7 @@ import {
 } from 'rxjs/operators';
 import { compareParamMaps, filterParamMap, isMissing, isPresent, NOP } from '../util';
 import { QueryParamGroup } from '../model/query-param-group';
-import { MultiQueryParam, QueryParam, PartitionedQueryParam } from '../model/query-param';
+import { MultiQueryParam, PartitionedQueryParam, QueryParam } from '../model/query-param';
 import { NGQP_ROUTER_ADAPTER, NGQP_ROUTER_OPTIONS, RouterAdapter, RouterOptions } from '../router-adapter/router-adapter.interface';
 import { QueryParamAccessor } from './query-param-accessor.interface';
 
@@ -227,31 +227,40 @@ export class QueryParamGroupService implements OnDestroy {
                 }),
             )),
             takeUntil(this.destroy$),
-        ).subscribe(queryParamMap => {
-            const synthetic = this.isSyntheticNavigation();
-            const groupValue: Record<string, unknown> = {};
-
-            Object.keys(this.getQueryParamGroup().queryParams).forEach(queryParamName => {
-                const partitionedQueryParam = this.getQueryParamAsPartition(queryParamName);
-                const newValues = partitionedQueryParam.queryParams.map(queryParam => isMultiQueryParam<unknown>(queryParam)
-                    ? queryParam.deserializeValue(queryParamMap.getAll(queryParam.urlParam))
-                    : queryParam.deserializeValue(queryParamMap.get(queryParam.urlParam))
+            switchMap(queryParamMap => {
+                const synthetic = this.isSyntheticNavigation();
+
+                return forkJoin(...Object.keys(this.getQueryParamGroup().queryParams).map(queryParamName => {
+                    const partitionedQueryParam = this.getQueryParamAsPartition(queryParamName);
+                    return forkJoin(...partitionedQueryParam.queryParams.map(queryParam => isMultiQueryParam<unknown>(queryParam)
+                        ? queryParam.deserializeValue(queryParamMap.getAll(queryParam.urlParam))
+                        : queryParam.deserializeValue(queryParamMap.get(queryParam.urlParam))
+                    )).pipe(
+                        map(newValues => partitionedQueryParam.reduce(newValues)),
+                        tap(newValue => {
+                            const directives = this.directives.get(queryParamName);
+                            if (directives) {
+                                directives.forEach(directive => directive.valueAccessor.writeValue(newValue));
+                            }
+                        }),
+                        map(newValue => {
+                            return { [ queryParamName ]: newValue };
+                        }),
+                    );
+                })).pipe(
+                    map((values: Record<string, unknown>[]) => values.reduce((groupValue, value) => {
+                        return {
+                            ...groupValue,
+                            ...value,
+                        };
+                    }, {})),
+                    tap(groupValue => this.getQueryParamGroup().setValue(groupValue, {
+                        emitEvent: !synthetic,
+                        emitModelToViewChange: false,
+                    })),
                 );
-                const newValue = partitionedQueryParam.reduce(newValues);
-
-                const directives = this.directives.get(queryParamName);
-                if (directives) {
-                    directives.forEach(directive => directive.valueAccessor.writeValue(newValue));
-                }
-
-                groupValue[ queryParamName ] = newValue;
-            });
-
-            this.getQueryParamGroup().setValue(groupValue, {
-                emitEvent: !synthetic,
-                emitModelToViewChange: false,
-            });
-        });
+            }),
+        ).subscribe();
     }
 
     /** Listens for newly added parameters and starts synchronization for them. */
@@ -350,7 +359,7 @@ export class QueryParamGroupService implements OnDestroy {
 
         return {
             ...(this.globalRouterOptions || {}),
-            ...groupOptions,
+            ...(groupOptions || {}),
         };
     }
 
diff --git a/projects/ngqp/core/src/lib/model/query-param.ts b/projects/ngqp/core/src/lib/model/query-param.ts
index 37b33b7..eeebd21 100644
--- a/projects/ngqp/core/src/lib/model/query-param.ts
+++ b/projects/ngqp/core/src/lib/model/query-param.ts
@@ -1,4 +1,4 @@
-import { Observable, Subject } from 'rxjs';
+import { forkJoin, isObservable, Observable, of, Subject } from 'rxjs';
 import { areEqualUsing, isFunction, isMissing, isPresent, undefinedToNull, wrapTryCatch } from '../util';
 import { Comparator, OnChangeFunction, ParamCombinator, ParamDeserializer, ParamSerializer, Partitioner, Reducer } from '../types';
 import { QueryParamGroup } from './query-param-group';
@@ -117,12 +117,6 @@ export abstract class AbstractQueryParam<U, T> extends AbstractQueryParamBase<T>
         this.combineWith = combineWith;
     }
 
-    /** @internal */
-    public abstract serializeValue(value: T | null): (string | null) | (string | null)[];
-
-    /** @internal */
-    public abstract deserializeValue(value: (string | null) | (string | null)[]): T | null;
-
     /**
      * Updates the value of this parameter.
      *
@@ -180,12 +174,17 @@ export class QueryParam<T> extends AbstractQueryParam<T | null, T | null> implem
     }
 
     /** @internal */
-    public deserializeValue(value: string | null): T | null {
+    public deserializeValue(value: string | null): Observable<T | null> {
         if (this.emptyOn !== undefined && value === null) {
-            return this.emptyOn;
+            return of(this.emptyOn);
         }
 
-        return this.deserialize(value);
+        const deserialized = this.deserialize(value);
+        if (isObservable<T | null>(deserialized)) {
+            return deserialized;
+        }
+
+        return of(deserialized);
     }
 
 }
@@ -212,12 +211,21 @@ export class MultiQueryParam<T> extends AbstractQueryParam<T | null, (T | null)[
     }
 
     /** @internal */
-    public deserializeValue(value: (string | null)[] | null): (T | null)[] | null {
+    public deserializeValue(value: (string | null)[] | null): Observable<(T | null)[] | null> {
         if (this.emptyOn !== undefined && (value || []).length === 0) {
-            return this.emptyOn;
+            return of(this.emptyOn);
         }
 
-        return (value || []).map(this.deserialize.bind(this));
+        return forkJoin<T | null>(...(value || [])
+            .map(v => {
+                const deserialized = this.deserialize(v);
+                if (isObservable<T | null>(deserialized)) {
+                    return deserialized;
+                }
+
+                return of(deserialized);
+            })
+        );
     }
 
 }
diff --git a/projects/ngqp/core/src/lib/types.ts b/projects/ngqp/core/src/lib/types.ts
index 1a168b9..1404782 100644
--- a/projects/ngqp/core/src/lib/types.ts
+++ b/projects/ngqp/core/src/lib/types.ts
@@ -1,4 +1,5 @@
 import { Params } from '@angular/router';
+import { Observable } from 'rxjs';
 
 /**
  * A serializer defines how the represented form control's
@@ -10,7 +11,7 @@ export type ParamSerializer<T> = (model: T | null) => string | null;
  * A deserializer defines how a URL parameter is converted
  * into the represented form control's value.
  */
-export type ParamDeserializer<T> = (value: string | null) => T | null;
+export type ParamDeserializer<T> = (value: string | null) => (T | null) | Observable<T | null>;
 
 /**
  * A partitioner can split a value into an array of parts.