diff --git a/lib/preprocessor.cpp b/lib/preprocessor.cpp
index 763ffe8e9..17ced4f87 100644
--- a/lib/preprocessor.cpp
+++ b/lib/preprocessor.cpp
@@ -611,7 +611,7 @@ std::string Preprocessor::getdef(std::string line, bool def)
     {
         const unsigned char chprev = (pos > 0) ? line[pos-1] : (unsigned char)0;
         const unsigned char chnext = (pos + 1 < line.length()) ? line[pos+1] : (unsigned char)0;
-        if (std::isalnum(chprev) && std::isalnum(chnext))
+        if ((std::isalnum(chprev) || chprev == '_') && (std::isalnum(chnext) || chnext == '_'))
             ++pos;
         else
             line.erase(pos, 1);
diff --git a/test/testpreprocessor.cpp b/test/testpreprocessor.cpp
index 44755f532..304bddbcc 100644
--- a/test/testpreprocessor.cpp
+++ b/test/testpreprocessor.cpp
@@ -104,6 +104,7 @@ private:
         TEST_CASE(if_cond6);
         TEST_CASE(if_cond7);
         TEST_CASE(if_cond8);
+        TEST_CASE(if_cond9);
 
         TEST_CASE(if_or);
 
@@ -871,6 +872,25 @@ private:
     }
 
 
+    void if_cond9()
+    {
+        const char filedata[] = "#if !defined _A\n"
+                                "abc\n"
+                                "#endif\n";
+
+        // Preprocess => actual result..
+        std::istringstream istr(filedata);
+        std::map<std::string, std::string> actual;
+        Settings settings;
+        Preprocessor preprocessor(&settings, this);
+        preprocessor.preprocess(istr, actual, "file.c");
+
+        // Compare results..
+        ASSERT_EQUALS(1, actual.size());
+        ASSERT_EQUALS("\nabc\n\n", actual[""]);
+    }
+
+
 
     void if_or()
     {