diff --git a/CHANGELOG.md b/CHANGELOG.md
index 78e73f8f..8d708e97 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2,6 +2,10 @@
 
 All notable changes to this project will be documented in this file.
 
+## Unreleased
+
+- Support config file locations other than project root, fixes [#1243](https://github.com/badeball/cypress-cucumber-preprocessor/discussions/1243).
+
 ## v21.0.0
 
 Breaking changes:
diff --git a/declarations.d.ts b/declarations.d.ts
index e0ee0f65..a2867bf8 100644
--- a/declarations.d.ts
+++ b/declarations.d.ts
@@ -4,9 +4,14 @@ declare module "find-cypress-specs" {
   export function getSpecs(
     config: Cypress.ConfigOptions,
     type: Cypress.TestingType,
+    returnAbsolute?: boolean,
   ): string[];
 
-  export function getSpecs(config: Cypress.PluginConfigOptions): string[];
+  export function getSpecs(
+    config: Cypress.PluginConfigOptions,
+    type: Cypress.TestingType,
+    returnAbsolute?: boolean,
+  ): string[];
 
   export function getConfig(): Cypress.ConfigOptions;
 }
diff --git a/features/issues/1243.feature b/features/issues/1243.feature
new file mode 100644
index 00000000..eecb58d2
--- /dev/null
+++ b/features/issues/1243.feature
@@ -0,0 +1,21 @@
+# https://github.com/badeball/cypress-cucumber-preprocessor/issues/1243
+
+Feature: custom config location
+  Scenario: custom config location
+    Given a file named "cypress/e2e/a.feature" with:
+      """
+      Feature: a feature
+        Scenario: a scenario
+          Given a step
+      """
+    And a file named "cypress/support/step_definitions/steps.js" with:
+      """
+      const { Given } = require("@badeball/cypress-cucumber-preprocessor");
+      Given("a step", function() {})
+      """
+    And a file named "config/cypress.config.js" with:
+      """
+      module.exports = require("../cypress.config.js");
+      """
+    When I run cypress with "--config-file config/cypress.config.js"
+    Then it passes
diff --git a/lib/add-cucumber-preprocessor-plugin.ts b/lib/add-cucumber-preprocessor-plugin.ts
index 5b7b19b9..7d6da74a 100644
--- a/lib/add-cucumber-preprocessor-plugin.ts
+++ b/lib/add-cucumber-preprocessor-plugin.ts
@@ -138,46 +138,48 @@ export async function addCucumberPreprocessorPlugin(
 
     const node = parse(tags);
 
-    const testFiles = getSpecs(config).filter((testFile) => {
-      if (!testFile.endsWith(".feature")) {
-        switch (preprocessor.filterSpecsMixedMode) {
-          case "hide":
-            return false;
-          case "show":
-            return true;
-          case "empty-set":
-            return node.evaluate([]);
-          default:
-            assertNever(preprocessor.filterSpecsMixedMode);
+    const testFiles = getSpecs(config, "foobar" as any, true).filter(
+      (testFile) => {
+        if (!testFile.endsWith(".feature")) {
+          switch (preprocessor.filterSpecsMixedMode) {
+            case "hide":
+              return false;
+            case "show":
+              return true;
+            case "empty-set":
+              return node.evaluate([]);
+            default:
+              assertNever(preprocessor.filterSpecsMixedMode);
+          }
         }
-      }
-
-      const content = fs.readFileSync(testFile).toString("utf-8");
-
-      const options = {
-        includeSource: false,
-        includeGherkinDocument: false,
-        includePickles: true,
-        newId: IdGenerator.incrementing(),
-      };
-
-      const envelopes = generateMessages(
-        content,
-        testFile,
-        SourceMediaType.TEXT_X_CUCUMBER_GHERKIN_PLAIN,
-        options,
-      );
-
-      const pickles = envelopes
-        .map((envelope) => envelope.pickle)
-        .filter(notNull);
-
-      return pickles.some((pickle) =>
-        node.evaluate(
-          pickle.tags?.map((tag) => tag.name).filter(notNull) ?? [],
-        ),
-      );
-    });
+
+        const content = fs.readFileSync(testFile).toString("utf-8");
+
+        const options = {
+          includeSource: false,
+          includeGherkinDocument: false,
+          includePickles: true,
+          newId: IdGenerator.incrementing(),
+        };
+
+        const envelopes = generateMessages(
+          content,
+          testFile,
+          SourceMediaType.TEXT_X_CUCUMBER_GHERKIN_PLAIN,
+          options,
+        );
+
+        const pickles = envelopes
+          .map((envelope) => envelope.pickle)
+          .filter(notNull);
+
+        return pickles.some((pickle) =>
+          node.evaluate(
+            pickle.tags?.map((tag) => tag.name).filter(notNull) ?? [],
+          ),
+        );
+      },
+    );
 
     debug(`Resolved specs ${inspect(testFiles)}`);
 
diff --git a/lib/step-definitions.ts b/lib/step-definitions.ts
index 3e7fc0ba..72979693 100644
--- a/lib/step-definitions.ts
+++ b/lib/step-definitions.ts
@@ -56,6 +56,22 @@ export function getStepDefinitionPatterns(
   >,
   filepath: string,
 ): string[] {
+  /**
+   * The reason for these assertions is that when giving relative paths to path.relative, the result
+   * will depend on CWD, which is affected by EG. the --config-file parameter [1].
+   *
+   * [1] https://github.com/badeball/cypress-cucumber-preprocessor/issues/1243
+   */
+  assert(
+    path.isAbsolute(configuration.implicitIntegrationFolder),
+    `Expected an absolute path for implicit integration folder but got ${configuration.implicitIntegrationFolder}`,
+  );
+
+  assert(
+    path.isAbsolute(filepath),
+    `Expected an absolute path for spec but got ${filepath}`,
+  );
+
   const filepathReplacement = glob.escape(
     trimFeatureExtension(
       path.relative(configuration.implicitIntegrationFolder, filepath),
diff --git a/lib/subpath-entrypoints/esbuild.ts b/lib/subpath-entrypoints/esbuild.ts
index 88d2b53a..f7cc6538 100644
--- a/lib/subpath-entrypoints/esbuild.ts
+++ b/lib/subpath-entrypoints/esbuild.ts
@@ -75,8 +75,6 @@ export function createEsbuildPlugin(
           if (needPrettify) {
             debug("esbuild: prettifying sources");
 
-            /**
-             */
             sourceMap.sources = sourceMap.sources.map((source: string) => {
               return path.relative(
                 configuration.projectRoot,
@@ -95,9 +93,17 @@ export function createEsbuildPlugin(
             "base64",
           );
 
+          /**
+           * Why `${"sourceMappingURL"}` you may ask. This is so esbuild doesn't crap itself upon
+           * errors, where it would search for source maps and find THIS code line, which is not a
+           * valid source map (obvously).
+           *
+           * Without this, esbuild would error with "Unexpected token z in JSON at position 0" every
+           * time an error occurred during build time.
+           */
           await fs.appendFile(
             outfile,
-            `//# sourceMappingURL=data:application/json;base64,${encoded}\n`,
+            `//# ${"sourceMappingURL"}=data:application/json;base64,${encoded}\n`,
           );
         });
       }
diff --git a/lib/template.ts b/lib/template.ts
index 3dcfe76c..6064d2e4 100644
--- a/lib/template.ts
+++ b/lib/template.ts
@@ -71,7 +71,11 @@ export async function compile(
   const pickles = envelopes.map((envelope) => envelope.pickle).filter(notNull);
 
   const implicitIntegrationFolder = assertAndReturn(
-    ancestor(...getSpecs(configuration).map(path.dirname).map(path.normalize)),
+    ancestor(
+      ...getSpecs(configuration, "foobar" as any, true)
+        .map(path.dirname)
+        .map(path.normalize),
+    ),
     "Expected to find a common ancestor path",
   );