diff --git a/website/src/util/formatUrl.ts b/website/src/util/formatUrl.ts
new file mode 100644
index 00000000..f01ad61c
--- /dev/null
+++ b/website/src/util/formatUrl.ts
@@ -0,0 +1,4 @@
+export function formatUrl(pathname: string, searchParams: URLSearchParams) {
+    const searchParamsString = searchParams.toString();
+    return `${pathname}${searchParamsString === '' ? '' : `?${searchParamsString}&`}`;
+}
diff --git a/website/src/views/covid.ts b/website/src/views/covid.ts
index dc26d81a..23b77b80 100644
--- a/website/src/views/covid.ts
+++ b/website/src/views/covid.ts
@@ -32,6 +32,7 @@ import { organismConfig, Organisms } from '../types/Organism.ts';
 import { type DataOrigin, dataOrigins } from '../types/dataOrigins.ts';
 import { SequencingEffortsStateHandler } from './pageStateHandlers/SequencingEffortsPageStateHandler.ts';
 import { SingleVariantPageStateHandler } from './pageStateHandlers/SingleVariantPageStateHandler.ts';
+import { formatUrl } from '../util/formatUrl.ts';
 
 const earliestDate = '2020-01-06';
 
@@ -164,7 +165,7 @@ class CovidSingleVariantStateHandler
         if (pageState.collectionId !== undefined) {
             search.set('collectionId', pageState.collectionId.toString());
         }
-        return `${this.pathname}?${search}`;
+        return formatUrl(this.pathname, search);
     }
 
     public override toLapisFilter(pageState: CovidVariantData) {
@@ -350,7 +351,8 @@ class CovidSequencingEffortsStateHandler
         if (pageState.collectionId !== undefined) {
             search.set('collectionId', pageState.collectionId.toString());
         }
-        return `${this.pathname}?${search}`;
+
+        return formatUrl(this.pathname, search);
     }
 
     public override toLapisFilter(pageState: CovidVariantData) {
diff --git a/website/src/views/pageStateHandlers/CompareSideBySidePageStateHandler.ts b/website/src/views/pageStateHandlers/CompareSideBySidePageStateHandler.ts
index 4f4b42e1..a6ddd0a7 100644
--- a/website/src/views/pageStateHandlers/CompareSideBySidePageStateHandler.ts
+++ b/website/src/views/pageStateHandlers/CompareSideBySidePageStateHandler.ts
@@ -18,6 +18,7 @@ import {
     searchParamsFromFilterMap,
     toLapisFilterWithoutVariant,
 } from './PageStateHandler.ts';
+import { formatUrl } from '../../util/formatUrl.ts';
 
 export abstract class CompareSideBySideStateHandler<ColumnData extends DatasetAndVariantData = DatasetAndVariantData>
     implements PageStateHandler<CompareSideBySideData<ColumnData>>
@@ -54,7 +55,7 @@ export abstract class CompareSideBySideStateHandler<ColumnData extends DatasetAn
             this.writeColumnDataToSearchParams(search, variant),
         );
 
-        return `${this.pathname}?${search}`;
+        return formatUrl(this.pathname, search);
     }
 
     public setFilter(
diff --git a/website/src/views/pageStateHandlers/CompareToBaselinePageStateHandler.ts b/website/src/views/pageStateHandlers/CompareToBaselinePageStateHandler.ts
index 9d541dc0..bb768dbc 100644
--- a/website/src/views/pageStateHandlers/CompareToBaselinePageStateHandler.ts
+++ b/website/src/views/pageStateHandlers/CompareToBaselinePageStateHandler.ts
@@ -26,6 +26,7 @@ import {
     toLapisFilterWithoutVariant,
 } from './PageStateHandler.ts';
 import type { VariantFilterConfig } from '../../components/pageStateSelectors/VariantFilterConfig.ts';
+import { formatUrl } from '../../util/formatUrl.ts';
 
 export class CompareToBaselineStateHandler implements PageStateHandler<CompareToBaselineData> {
     protected readonly pathname;
@@ -84,7 +85,7 @@ export class CompareToBaselineStateHandler implements PageStateHandler<CompareTo
             getLineageFilterFields(this.constants.lineageFilters),
         );
 
-        return `${this.pathname}?${search}`;
+        return formatUrl(this.pathname, search);
     }
 
     public datasetFilterToLapisFilter(baselineFilter: DatasetFilter): LapisFilter {
diff --git a/website/src/views/pageStateHandlers/CompareVariantsPageStateHandler.ts b/website/src/views/pageStateHandlers/CompareVariantsPageStateHandler.ts
index 54c10fb1..0c7fe632 100644
--- a/website/src/views/pageStateHandlers/CompareVariantsPageStateHandler.ts
+++ b/website/src/views/pageStateHandlers/CompareVariantsPageStateHandler.ts
@@ -26,6 +26,7 @@ import {
     toLapisFilterWithoutVariant,
 } from './PageStateHandler.ts';
 import type { VariantFilterConfig } from '../../components/pageStateSelectors/VariantFilterConfig.ts';
+import { formatUrl } from '../../util/formatUrl.ts';
 
 export class CompareVariantsPageStateHandler implements PageStateHandler<CompareVariantsData> {
     protected readonly pathname;
@@ -75,7 +76,7 @@ export class CompareVariantsPageStateHandler implements PageStateHandler<Compare
             setSearchFromDateRange(search, this.constants.mainDateField, pageState.datasetFilter.dateRange);
         }
 
-        return `${this.pathname}?${search}`;
+        return formatUrl(this.pathname, search);
     }
 
     public datasetFilterToLapisFilter(datasetFilter: DatasetFilter): LapisFilter {
diff --git a/website/src/views/pageStateHandlers/SequencingEffortsPageStateHandler.ts b/website/src/views/pageStateHandlers/SequencingEffortsPageStateHandler.ts
index 6331afd3..3bf54dca 100644
--- a/website/src/views/pageStateHandlers/SequencingEffortsPageStateHandler.ts
+++ b/website/src/views/pageStateHandlers/SequencingEffortsPageStateHandler.ts
@@ -10,6 +10,7 @@ import {
     setSearchFromLocation,
 } from '../helpers.ts';
 import { type PageStateHandler, toLapisFilterWithoutVariant } from './PageStateHandler.ts';
+import { formatUrl } from '../../util/formatUrl.ts';
 
 export class SequencingEffortsStateHandler<PageState extends DatasetAndVariantData = DatasetAndVariantData>
     implements PageStateHandler<DatasetAndVariantData>
@@ -48,7 +49,7 @@ export class SequencingEffortsStateHandler<PageState extends DatasetAndVariantDa
             pageState.variantFilter,
             getLineageFilterFields(this.constants.lineageFilters),
         );
-        return `${this.pathname}?${search}`;
+        return formatUrl(this.pathname, search);
     }
 
     public toLapisFilter(pageState: DatasetAndVariantData) {
diff --git a/website/src/views/pageStateHandlers/SingleVariantPageStateHandler.ts b/website/src/views/pageStateHandlers/SingleVariantPageStateHandler.ts
index ee184a16..af1f78f6 100644
--- a/website/src/views/pageStateHandlers/SingleVariantPageStateHandler.ts
+++ b/website/src/views/pageStateHandlers/SingleVariantPageStateHandler.ts
@@ -13,6 +13,7 @@ import {
     setSearchFromLocation,
 } from '../helpers.ts';
 import { type PageStateHandler, toLapisFilterWithoutVariant } from './PageStateHandler.ts';
+import { formatUrl } from '../../util/formatUrl.ts';
 
 export class SingleVariantPageStateHandler<PageState extends DatasetAndVariantData = DatasetAndVariantData>
     implements PageStateHandler<DatasetAndVariantData>
@@ -51,7 +52,7 @@ export class SingleVariantPageStateHandler<PageState extends DatasetAndVariantDa
             pageState.variantFilter,
             getLineageFilterFields(this.constants.lineageFilters),
         );
-        return `${this.pathname}?${search}`;
+        return formatUrl(this.pathname, search);
     }
 
     public toLapisFilter(pageState: DatasetAndVariantData) {