diff --git a/src/main/java/me/itzg/helpers/curseforge/CurseForgeApiClient.java b/src/main/java/me/itzg/helpers/curseforge/CurseForgeApiClient.java
index 0430e39b..3971a401 100644
--- a/src/main/java/me/itzg/helpers/curseforge/CurseForgeApiClient.java
+++ b/src/main/java/me/itzg/helpers/curseforge/CurseForgeApiClient.java
@@ -51,13 +51,13 @@ public class CurseForgeApiClient implements AutoCloseable {
 
     public CurseForgeApiClient(String apiBaseUrl, String apiKey, SharedFetch.Options sharedFetchOptions, String gameId
     ) {
-        if (apiKey == null || apiKey.isEmpty()) {
+        if (apiKey == null || apiKey.trim().isEmpty()) {
             throw new InvalidParameterException("CurseForge API key is required");
         }
 
         this.preparedFetch = Fetch.sharedFetch("install-curseforge",
             (sharedFetchOptions != null ? sharedFetchOptions : SharedFetch.Options.builder().build())
-                .withHeader(API_KEY_HEADER, apiKey)
+                .withHeader(API_KEY_HEADER, apiKey.trim())
         );
         this.uriBuilder = UriBuilder.withBaseUrl(apiBaseUrl);
         this.gameId = gameId;
diff --git a/src/test/java/me/itzg/helpers/curseforge/CurseForgeApiClientTest.java b/src/test/java/me/itzg/helpers/curseforge/CurseForgeApiClientTest.java
new file mode 100644
index 00000000..27f86420
--- /dev/null
+++ b/src/test/java/me/itzg/helpers/curseforge/CurseForgeApiClientTest.java
@@ -0,0 +1,40 @@
+package me.itzg.helpers.curseforge;
+
+import static com.github.tomakehurst.wiremock.client.WireMock.*;
+import static org.assertj.core.api.Assertions.assertThat;
+
+import com.github.tomakehurst.wiremock.junit5.WireMockRuntimeInfo;
+import com.github.tomakehurst.wiremock.junit5.WireMockTest;
+import java.util.Collections;
+import me.itzg.helpers.http.SharedFetch.Options;
+import org.intellij.lang.annotations.Language;
+import org.junit.jupiter.api.Test;
+
+@WireMockTest
+class CurseForgeApiClientTest {
+
+    @Test
+    void apiKeyHeaderIsTrimmed(WireMockRuntimeInfo wmInfo) {
+        @Language("JSON") final String body = "{\"data\": []}";
+        stubFor(get("/v1/categories?gameId=test&classesOnly=true")
+            .willReturn(aResponse()
+                .withBody(body)
+                .withHeader("Content-Type", "application/json")
+            )
+        );
+
+        final CategoryInfo result;
+        try (CurseForgeApiClient client = new CurseForgeApiClient(wmInfo.getHttpBaseUrl(), "key\n", Options.builder().build(),
+            "test"
+        )) {
+            result = client.loadCategoryInfo(Collections.singleton("mc-mods"))
+                .block();
+        }
+
+        assertThat(result).isNotNull();
+
+        verify(getRequestedFor(urlEqualTo("/v1/categories?gameId=test&classesOnly=true"))
+            .withHeader("x-api-key", equalTo("key"))
+        );
+    }
+}
\ No newline at end of file