diff --git a/src/solc.ts b/src/solc.ts
index 77f7be7a..afa8d47e 100644
--- a/src/solc.ts
+++ b/src/solc.ts
@@ -44,6 +44,26 @@ function tidy(_line: string) {
   return line;
 }
 
+type PathModule = Pick<typeof path, 'relative' | 'sep'>;
+
+/**
+ * Build the source-map key for an imported Solidity file.
+ *
+ * solc's `findImports` callback always receives '/'-separated import paths, so
+ * the keys we register in the sources map must use '/' as well. `path.relative`
+ * returns OS-native separators — '/' on POSIX but '\' on Windows — so we
+ * normalise here. On POSIX this is a no-op; on Windows it converts the '\'
+ * separators that would otherwise cause "couldn't find the import" failures.
+ *
+ * `p` is injectable purely so this can be unit-tested deterministically for both
+ * `path.posix` and `path.win32` regardless of the host OS.
+ */
+export const toImportKey = (
+  topDir: string,
+  importPath: string,
+  p: PathModule = path,
+): string => p.relative(topDir, importPath).split(p.sep).join('/');
+
 const buildSources = (file: any, options: any) => {
   const sources = {};
   const contractsFiles = [];
@@ -60,7 +80,8 @@ const buildSources = (file: any, options: any) => {
           relPath,
         );
 
-        relPath = path.relative(options.topDir, importPath);
+        // Normalise to '/' so this key matches what solc passes to findImports.
+        relPath = toImportKey(options.topDir, importPath);
 
         contractsFiles.push([importPath, relPath]);
       }
diff --git a/test/solc-import-path.test.js b/test/solc-import-path.test.js
new file mode 100644
index 00000000..5a0f6fdb
--- /dev/null
+++ b/test/solc-import-path.test.js
@@ -0,0 +1,34 @@
+import assert from 'assert';
+import path from 'path';
+import { toImportKey } from '../built/solc.js';
+
+/**
+ * Regression tests for import-path resolution in src/solc.ts (buildSources).
+ *
+ * solc's `findImports` callback always receives '/'-separated paths, so the keys
+ * we register in the sources map must use '/' too. `path.relative` returns
+ * OS-native separators, so `toImportKey` normalises them. The Windows case is
+ * exercised with `path.win32` explicitly, so it runs identically on a Linux CI
+ * and FAILS without the `.split(p.sep).join('/')` normalisation.
+ */
+describe('solc import-path key normalisation', function () {
+  const importPathPosix = '/home/dev/contracts/Escrow-imports/IERC20.sol';
+  const topDirPosix = '/home/dev/contracts';
+
+  const importPathWin = 'C:\\Users\\dev\\contracts\\Escrow-imports\\IERC20.sol';
+  const topDirWin = 'C:\\Users\\dev\\contracts';
+
+  const expected = 'Escrow-imports/IERC20.sol';
+
+  it('Linux/POSIX: yields a forward-slash import key', function () {
+    const key = toImportKey(topDirPosix, importPathPosix, path.posix);
+    assert.strictEqual(key, expected);
+  });
+
+  it('Windows: yields a forward-slash import key (fails without the fix)', function () {
+    // Without normalisation this would be 'Escrow-imports\\IERC20.sol', which
+    // never matches solc's '/'-separated key -> "couldn't find the import".
+    const key = toImportKey(topDirWin, importPathWin, path.win32);
+    assert.strictEqual(key, expected);
+  });
+});