diff --git a/system/host/fidl/include/fidl/error_reporter.h b/system/host/fidl/include/fidl/error_reporter.h
index c323ce2..7816742 100644
--- a/system/host/fidl/include/fidl/error_reporter.h
+++ b/system/host/fidl/include/fidl/error_reporter.h
@@ -8,11 +8,17 @@
 #include <string>
 #include <vector>
 
+#include "source_location.h"
+#include "string_view.h"
+#include "token.h"
+
 namespace fidl {
 
 class ErrorReporter {
 public:
-    void ReportError(std::string error);
+    void ReportError(const SourceLocation& location, StringView message);
+    void ReportError(const Token& token, StringView message);
+    void ReportError(StringView message);
     void PrintReports();
     const std::vector<std::string>& errors() const { return errors_; };
 
diff --git a/system/host/fidl/lib/error_reporter.cpp b/system/host/fidl/lib/error_reporter.cpp
index 1779088..72df693 100644
--- a/system/host/fidl/lib/error_reporter.cpp
+++ b/system/host/fidl/lib/error_reporter.cpp
@@ -3,16 +3,90 @@
 // found in the LICENSE file.
 
 #include "fidl/error_reporter.h"
+#include "fidl/source_location.h"
+#include "fidl/string_view.h"
+#include "fidl/token.h"
 
 namespace fidl {
 
-void ErrorReporter::ReportError(std::string error) {
+std::string MakeSquiggle(const std::string& surrounding_line, int column) {
+    std::string squiggle;
+    for (int i = 0; i < column; i++) {
+        switch (surrounding_line[i]) {
+        case '\t':
+            squiggle.push_back('\t');
+        default:
+            squiggle.push_back(' ');
+        }
+    }
+    squiggle.push_back('^');
+    return squiggle;
+}
+
+std::string FormatError(const SourceLocation& location, StringView message, size_t squiggle_size = 0u) {
+    SourceFile::Position position;
+    std::string surrounding_line = location.SourceLine(&position);
+
+    std::string squiggle = MakeSquiggle(surrounding_line, position.column);
+    if (squiggle_size != 0u) {
+        --squiggle_size;
+    }
+    squiggle += std::string(squiggle_size, '~');
+    // Some tokens (like string literals) can span multiple
+    // lines. Truncate the string to just one line at most. The
+    // containing line contains a newline, so drop it when
+    // comparing sizes.
+    size_t line_size = surrounding_line.size() - 1;
+    if (squiggle.size() > line_size) {
+        squiggle.resize(line_size);
+    }
+
+    // Many editors and IDEs recognize errors in the form of
+    // filename:linenumber:column: error: descriptive-test-here\n
+    std::string error = location.position();
+    error.append(": error: ");
+    error.append(message);
+    error.push_back('\n');
+    error.append(surrounding_line);
+    error.append(squiggle);
+
+    return error;
+}
+
+// ReportError records an error with the location, message, source line, and
+// position indicator.
+//
+//     filename:line:col: error: message
+//     sourceline
+//        ^
+void ErrorReporter::ReportError(const SourceLocation& location, StringView message) {
+    auto error = FormatError(location, message);
+    errors_.push_back(std::move(error));
+}
+
+// ReportError records an error with the location, message, source line,
+// position indicator, and tildes under the token reported.
+//
+//     filename:line:col: error: message
+//     sourceline
+//        ^~~~
+void ErrorReporter::ReportError(const Token& token, StringView message) {
+    auto token_location = token.location();
+    auto token_data = token_location.data();
+    auto error = FormatError(token_location, message, token_data.size());
+    errors_.push_back(std::move(error));
+}
+
+// ReportError records the provided message.
+void ErrorReporter::ReportError(StringView message) {
+    std::string error("error: ");
+    error.append(message);
     errors_.push_back(std::move(error));
 }
 
 void ErrorReporter::PrintReports() {
     for (const auto& error : errors_) {
-        fprintf(stderr, "%s", error.data());
+        fprintf(stderr, "%s\n", error.data());
     }
 }
 
diff --git a/system/host/fidl/lib/flat_ast.cpp b/system/host/fidl/lib/flat_ast.cpp
index 369cb5f..f36ccd4 100644
--- a/system/host/fidl/lib/flat_ast.cpp
+++ b/system/host/fidl/lib/flat_ast.cpp
@@ -365,16 +365,12 @@
 }
 
 bool Library::Fail(StringView message) {
-    auto formatted_message = std::string(message) + "\n";
-    error_reporter_->ReportError(std::move(formatted_message));
+    error_reporter_->ReportError(message);
     return false;
 }
 
 bool Library::Fail(const SourceLocation& location, StringView message) {
-    // Many editors and IDEs recognize errors in the form of
-    // filename:linenumber:column: error: descriptive-test-here\n
-    auto formatted_message = location.position() + ": error: " + std::string(message) + "\n";
-    error_reporter_->ReportError(std::move(formatted_message));
+    error_reporter_->ReportError(location, message);
     return false;
 }
 
diff --git a/system/host/fidl/lib/parser.cpp b/system/host/fidl/lib/parser.cpp
index 6d2ba77..e7a39fd 100644
--- a/system/host/fidl/lib/parser.cpp
+++ b/system/host/fidl/lib/parser.cpp
@@ -79,59 +79,13 @@
     return true;
 }
 
-std::string MakeSquiggle(const std::string& surrounding_line, int column) {
-    std::string squiggle;
-    for (int i = 0; i < column - 1; i++) {
-        switch (surrounding_line[i]) {
-        case '\t':
-            squiggle += "\t";
-        default:
-            squiggle += " ";
-        }
-    }
-    squiggle += "^";
-    return squiggle;
-}
-
 decltype(nullptr) Parser::Fail() {
   return Fail("found unexpected token");
 }
 
 decltype(nullptr) Parser::Fail(StringView message) {
     if (ok_) {
-        auto token_location = last_token_.location();
-        auto token_data = token_location.data();
-
-        SourceFile::Position position;
-        std::string surrounding_line = token_location.SourceLine(&position);
-        auto line_number = std::to_string(position.line);
-        auto column_number = std::to_string(position.column);
-
-        std::string squiggle = MakeSquiggle(surrounding_line, position.column);
-        size_t squiggle_size = token_data.size();
-        if (squiggle_size != 0u) {
-            --squiggle_size;
-        }
-        squiggle += std::string(squiggle_size, '~');
-        // Some tokens (like string literals) can span multiple
-        // lines. Truncate the string to just one line at most. The
-        // containing line contains a newline, so drop it when
-        // comparing sizes.
-        size_t line_size = surrounding_line.size() - 1;
-        if (squiggle.size() > line_size) {
-            squiggle.resize(line_size);
-        }
-
-        // Many editors and IDEs recognize errors in the form of
-        // filename:linenumber:column: error: descriptive-test-here\n
-        std::string error = token_location.position();
-        error += ": error: ";
-        error += message;
-        error += "\n";
-        error += surrounding_line;
-        error += squiggle + "\n";
-
-        error_reporter_->ReportError(std::move(error));
+        error_reporter_->ReportError(last_token_, std::move(message));
         ok_ = false;
     }
     return nullptr;
diff --git a/system/utest/fidl-compiler/using_tests.cpp b/system/utest/fidl-compiler/using_tests.cpp
index e6d4a37..5b8c6c7 100644
--- a/system/utest/fidl-compiler/using_tests.cpp
+++ b/system/utest/fidl-compiler/using_tests.cpp
@@ -93,11 +93,8 @@
     ASSERT_FALSE(library.Compile());
     const auto& errors = library.errors();
     ASSERT_EQ(1, errors.size());
-    // TODO(pascal): Refactor. We should check the error message, not
-    // necessarily the formatted message with filename:linenum:colnum. Consider
-    // introducing ASSERT_STR_CONTAINS.
-    ASSERT_STR_EQ(errors[0].c_str(),
-        "uzing.fidl:7:2: error: Unknown dependent library fidl.test.uzing.dependent. Did you require it with `using`?\n");
+    ASSERT_STR_STR(errors[0].c_str(),
+        "Unknown dependent library fidl.test.uzing.dependent. Did you require it with `using`?");
 
     END_TEST;
 }
@@ -124,11 +121,8 @@
     ASSERT_FALSE(library.Compile());
     const auto& errors = library.errors();
     ASSERT_EQ(1, errors.size());
-    // TODO(pascal): Refactor. We should check the error message, not
-    // necessarily the formatted message with filename:linenum:colnum. Consider
-    // introducing ASSERT_STR_CONTAINS.
-    ASSERT_STR_EQ(errors[0].c_str(),
-        "Library fidl.test.uzing.dependent already imported. Did you require it twice?\n");
+    ASSERT_STR_STR(errors[0].c_str(),
+        "Library fidl.test.uzing.dependent already imported. Did you require it twice?");
 
     END_TEST;
 }