diff --git a/libsolc/libsolc.cpp b/libsolc/libsolc.cpp
index 060baaa2a..29b732156 100644
--- a/libsolc/libsolc.cpp
+++ b/libsolc/libsolc.cpp
@@ -53,7 +53,7 @@ ReadCallback::Callback wrapReadCallback(CStyleReadFileCallback _readCallback = n
 			if (!contents_c && !error_c)
 			{
 				result.success = false;
-				result.responseOrErrorMessage = "File not found.";
+				result.responseOrErrorMessage = "Callback not supported.";
 			}
 			if (contents_c)
 			{
diff --git a/libsolc/libsolc.h b/libsolc/libsolc.h
index 2c55c2342..a4ca377a2 100644
--- a/libsolc/libsolc.h
+++ b/libsolc/libsolc.h
@@ -36,7 +36,13 @@ extern "C" {
 
 /// Callback used to retrieve additional source files.
 ///
-/// "Returns" two pointers that should be heap-allocated and are free'd by the caller.
+/// @param _path The path for loading.
+/// @param o_contents A pointer to the contents of the file, if found.
+/// @param o_error A pointer to an error message, if there is one.
+///
+/// If the callback is not supported, o_contents and o_error should be set to NULL.
+///
+/// The two pointers (o_contents and o_error) should be heap-allocated and are free'd by the caller.
 typedef void (*CStyleReadFileCallback)(char const* _path, char** o_contents, char** o_error);
 
 /// Returns the complete license document.
@@ -52,7 +58,10 @@ char const* solidity_version() SOLC_NOEXCEPT;
 /// Takes a "Standard Input JSON" and an optional callback (can be set to null). Returns
 /// a "Standard Output JSON". Both are to be UTF-8 encoded.
 ///
-/// The pointer returned must not be freed by the caller.
+/// @param _input
+/// @param _readCallback
+///
+/// @returns A pointer to the result. The pointer returned must not be freed by the caller.
 char const* solidity_compile(char const* _input, CStyleReadFileCallback _readCallback) SOLC_NOEXCEPT;
 
 /// Frees up any allocated memory.
diff --git a/test/libsolidity/LibSolc.cpp b/test/libsolidity/LibSolc.cpp
index b94486ac8..3f55cdaed 100644
--- a/test/libsolidity/LibSolc.cpp
+++ b/test/libsolidity/LibSolc.cpp
@@ -167,7 +167,7 @@ BOOST_AUTO_TEST_CASE(with_callback)
 	BOOST_CHECK(containsError(result, "ParserError", "Source \"missing.sol\" not found: Missing file."));
 
 	// This should be placed due to the missing "notfound.sol" which sets both pointers to null.
-	BOOST_CHECK(containsError(result, "ParserError", "Source \"notfound.sol\" not found: File not found."));
+	BOOST_CHECK(containsError(result, "ParserError", "Source \"notfound.sol\" not found: Callback not supported."));
 }
 
 BOOST_AUTO_TEST_SUITE_END()