diff --git a/main.cpp b/main.cpp
index ecbe062f..ae0bfccf 100644
--- a/main.cpp
+++ b/main.cpp
@@ -120,6 +120,10 @@ int main(int argc, char **argv)
             std::cout << "error: could not open file '" << filename << "'" << std::endl;
             std::exit(1);
         }
+        if (!simplecpp::isFile(filename)) {
+            std::cout << "error: could not open file '" << filename << "' - not a regular file" << std::endl;
+            std::exit(1);
+        }
         rawtokens = new simplecpp::TokenList(f, files,filename,&outputList);
     }
     else {
diff --git a/simplecpp.cpp b/simplecpp.cpp
index 3c63835a..59f94824 100755
--- a/simplecpp.cpp
+++ b/simplecpp.cpp
@@ -3026,9 +3026,11 @@ static std::string openHeader(std::ifstream &f, const std::string &path)
     if (nonExistingFilesCache.contains(simplePath))
         return "";  // file is known not to exist, skip expensive file open call
 #endif
-    f.open(simplePath.c_str());
-    if (f.is_open())
-        return simplePath;
+    if (simplecpp::isFile(simplePath)) {
+        f.open(simplePath.c_str());
+        if (f.is_open())
+            return simplePath;
+    }
 #ifdef SIMPLECPP_WINDOWS
     nonExistingFilesCache.add(simplePath);
 #endif
@@ -3131,18 +3133,19 @@ std::map<std::string, simplecpp::TokenList*> simplecpp::load(const simplecpp::To
         if (ret.find(filename) != ret.end())
             continue;
 
-        std::ifstream fin(filename.c_str());
-        if (!fin.is_open()) {
-            if (outputList) {
-                simplecpp::Output err(filenames);
-                err.type = simplecpp::Output::EXPLICIT_INCLUDE_NOT_FOUND;
-                err.location = Location(filenames);
-                err.msg = "Can not open include file '" + filename + "' that is explicitly included.";
-                outputList->push_back(err);
+        {
+            std::ifstream fin(filename.c_str());
+            if (!fin.is_open() || !isFile(filename)) {
+                if (outputList) {
+                    simplecpp::Output err(filenames);
+                    err.type = simplecpp::Output::EXPLICIT_INCLUDE_NOT_FOUND;
+                    err.location = Location(filenames);
+                    err.msg = "Can not open include file '" + filename + "' that is explicitly included.";
+                    outputList->push_back(err);
+                }
+                continue;
             }
-            continue;
         }
-        fin.close();
 
         TokenList *tokenlist = new TokenList(filename, filenames, outputList);
         if (!tokenlist->front()) {
diff --git a/test.cpp b/test.cpp
index 9588441c..804114f6 100644
--- a/test.cpp
+++ b/test.cpp
@@ -1776,6 +1776,26 @@ static void missingHeader3()
     ASSERT_EQUALS("", toString(outputList));
 }
 
+#ifndef _WIN32
+static void missingHeader4()
+{
+    // this is a directory
+    const char code[] = "#include \"/\"\n";
+    simplecpp::OutputList outputList;
+    ASSERT_EQUALS("", preprocess(code, &outputList));
+    ASSERT_EQUALS("file0,1,missing_header,Header not found: \"/\"\n", toString(outputList));
+}
+
+static void missingHeader5()
+{
+    // this is a directory
+    const char code[] = "#include \"/usr\"\n";
+    simplecpp::OutputList outputList;
+    ASSERT_EQUALS("", preprocess(code, &outputList));
+    ASSERT_EQUALS("file0,1,missing_header,Header not found: \"/usr\"\n", toString(outputList));
+}
+#endif
+
 static void nestedInclude()
 {
     const char code[] = "#include \"test.h\"\n";
@@ -2867,6 +2887,10 @@ int main(int argc, char **argv)
     TEST_CASE(missingHeader1);
     TEST_CASE(missingHeader2);
     TEST_CASE(missingHeader3);
+#ifndef _WIN32
+    TEST_CASE(missingHeader4);
+    TEST_CASE(missingHeader5);
+#endif
     TEST_CASE(nestedInclude);
     TEST_CASE(systemInclude);