diff --git a/languages/clang/clangparsejob.cpp b/languages/clang/clangparsejob.cpp
--- a/languages/clang/clangparsejob.cpp
+++ b/languages/clang/clangparsejob.cpp
@@ -52,6 +52,7 @@
 #include "duchain/clangparsingenvironmentfile.h"
 #include "util/clangdebug.h"
 #include "util/clangtypes.h"
+#include "util/clangutils.h"
 
 #include "clangsupport.h"
 #include "duchain/documentfinderhelpers.h"
@@ -191,21 +192,18 @@
     }
     m_environment.setProjectPaths(projectPaths);
 
+    m_unsavedFiles = ClangUtils::unsavedFiles();
+
     foreach(auto document, ICore::self()->documentController()->openDocuments()) {
         auto textDocument = document->textDocument();
-        // TODO: Introduce a cache so we don't have to re-read all the open documents
-        // which were not changed since the last run
-        if (!textDocument || !textDocument->url().isLocalFile()
-            || !DocumentFinderHelpers::mimeTypesList().contains(textDocument->mimeType()))
-        {
+        if ( !textDocument ) {
             continue;
         }
-        m_unsavedFiles << UnsavedFile(textDocument->url().toLocalFile(), textDocument->textLines(textDocument->documentRange()));
         const IndexedString indexedUrl(textDocument->url());
-        m_unsavedRevisions.insert(indexedUrl, ModificationRevision::revisionForFile(indexedUrl));
         if (indexedUrl == tuUrl) {
             m_tuDocumentIsUnsaved = true;
         }
+        m_unsavedRevisions.insert(indexedUrl, ModificationRevision::revisionForFile(indexedUrl));
     }
 
     if (auto tracker = trackerForUrl(url)) {
diff --git a/languages/clang/codecompletion/context.cpp b/languages/clang/codecompletion/context.cpp
--- a/languages/clang/codecompletion/context.cpp
+++ b/languages/clang/codecompletion/context.cpp
@@ -42,11 +42,14 @@
 #include <language/duchain/types/typeutils.h>
 #include <language/codecompletion/codecompletionmodel.h>
 #include <language/codecompletion/normaldeclarationcompletionitem.h>
+#include <util/foregroundlock.h>
 
 #include "../util/clangdebug.h"
 #include "../util/clangtypes.h"
+#include "../util/clangutils.h"
 #include "../duchain/clangdiagnosticevaluator.h"
 #include "../duchain/parsesession.h"
+#include "../duchain/duchainutils.h"
 #include "../duchain/navigationwidget.h"
 #include "../clangsettings/clangsettingsmanager.h"
 
@@ -775,18 +778,31 @@
     qRegisterMetaType<MemberAccessReplacer::Type>();
     const QByteArray file = url.toLocalFile().toUtf8();
     ParseSession session(m_parseSessionData);
+
+    QVector<UnsavedFile> otherUnsavedFiles;
+    {
+        ForegroundLock lock;
+        otherUnsavedFiles = ClangUtils::unsavedFiles();
+    }
+    QVector<CXUnsavedFile> allUnsaved;
+
     {
         const unsigned int completeOptions = clang_defaultCodeCompleteOptions();
 
         CXUnsavedFile unsaved;
         unsaved.Filename = file.constData();
         const QByteArray content = m_text.toUtf8();
         unsaved.Contents = content.constData();
-        unsaved.Length = content.size() + 1; // + \0-byte
+        unsaved.Length = content.size();
+
+        for ( const auto& f : otherUnsavedFiles ) {
+            allUnsaved.append(f.toClangApi());
+        }
+        allUnsaved.append(unsaved);
 
         m_results.reset(clang_codeCompleteAt(session.unit(), file.constData(),
                         position.line() + 1, position.column() + 1,
-                        content.isEmpty() ? nullptr : &unsaved, content.isEmpty() ? 0 : 1,
+                        allUnsaved.data(), allUnsaved.size(),
                         completeOptions));
 
         if (!m_results) {
@@ -833,11 +849,12 @@
             unsaved.Filename = file.constData();
             const QByteArray content = m_text.toUtf8();
             unsaved.Contents = content.constData();
-            unsaved.Length = content.size() + 1;
+            unsaved.Length = content.size();
+            allUnsaved[allUnsaved.size() - 1] = unsaved;
 
             m_results.reset(clang_codeCompleteAt(session.unit(), file.constData(),
                                                  position.line() + 1, position.column() + 1 + 1,
-                                                 &unsaved, 1,
+                                                 allUnsaved.data(), allUnsaved.size(),
                                                  clang_defaultCodeCompleteOptions()));
 
             if (m_results && m_results->NumResults) {
diff --git a/languages/clang/duchain/parsesession.cpp b/languages/clang/duchain/parsesession.cpp
--- a/languages/clang/duchain/parsesession.cpp
+++ b/languages/clang/duchain/parsesession.cpp
@@ -183,8 +183,7 @@
     : m_file(nullptr)
     , m_unit(nullptr)
 {
-    unsigned int flags = CXTranslationUnit_CXXChainedPCH
-        | CXTranslationUnit_DetailedPreprocessingRecord
+    unsigned int flags = CXTranslationUnit_DetailedPreprocessingRecord
 #if CINDEX_VERSION_MINOR >= 34
         | CXTranslationUnit_KeepGoing
 #endif
@@ -196,6 +195,9 @@
         flags |= CXTranslationUnit_ForSerialization;
     } else {
         flags |= CXTranslationUnit_CacheCompletionResults
+#if CINDEX_VERSION_MINOR >= 32
+              |  CXTranslationUnit_CreatePreambleOnFirstParse
+#endif
               |  CXTranslationUnit_PrecompiledPreamble;
         if (environment.quality() == ClangParsingEnvironment::Unknown) {
             flags |= CXTranslationUnit_Incomplete;
diff --git a/languages/clang/util/clangutils.h b/languages/clang/util/clangutils.h
--- a/languages/clang/util/clangutils.h
+++ b/languages/clang/util/clangutils.h
@@ -29,6 +29,7 @@
 #include <clang-c/Index.h>
 
 #include "clangprivateexport.h"
+#include "../duchain/unsavedfile.h"
 
 namespace ClangUtils
 {
@@ -70,6 +71,16 @@
     bool isScopeKind(CXCursorKind kind);
 
     /**
+     * @brief Retrieve a list of all unsaved files.
+     *
+     * @note Since this reads text from the editor widget, it must be called from the
+     *       GUI thread or with the foreground lock held.
+     *
+     * @return vector of all unsaved files and their current contents
+     */
+    KDEVCLANGPRIVATE_EXPORT QVector<UnsavedFile> unsavedFiles();
+
+    /**
      * Given a cursor and destination context, returns the string representing the
      * cursor's scope at its current location.
      *
diff --git a/languages/clang/util/clangutils.cpp b/languages/clang/util/clangutils.cpp
--- a/languages/clang/util/clangutils.cpp
+++ b/languages/clang/util/clangutils.cpp
@@ -24,8 +24,11 @@
 #include "../util/clangdebug.h"
 #include "../util/clangtypes.h"
 #include "../duchain/cursorkindtraits.h"
+#include "../duchain/documentfinderhelpers.h"
 
 #include <language/duchain/stringhelpers.h>
+#include <interfaces/icore.h>
+#include <interfaces/idocumentcontroller.h>
 
 #include <clang-c/Index.h>
 
@@ -52,6 +55,27 @@
     return clang_getCursor(unit, location);
 }
 
+QVector<UnsavedFile> ClangUtils::unsavedFiles()
+{
+    QVector<UnsavedFile> ret;
+    foreach(auto document, ICore::self()->documentController()->openDocuments()) {
+        auto textDocument = document->textDocument();
+        // TODO: Introduce a cache so we don't have to re-read all the open documents
+        // which were not changed since the last run
+        if (!textDocument || !textDocument->url().isLocalFile()
+            || !DocumentFinderHelpers::mimeTypesList().contains(textDocument->mimeType()))
+        {
+            continue;
+        }
+        if (!textDocument->isModified()) {
+            continue;
+        }
+        ret << UnsavedFile(textDocument->url().toLocalFile(),
+                           textDocument->textLines(textDocument->documentRange()));
+    }
+    return ret;
+}
+
 KTextEditor::Range ClangUtils::rangeForIncludePathSpec(const QString& line, const KTextEditor::Range& originalRange)
 {
     static const QRegularExpression pattern(QStringLiteral("^\\s*(#include|#import)"));