diff --git a/src/backend/utils/misc/guc-file.l b/src/backend/utils/misc/guc-file.l
index afe4fe6d775..581507a7696 100644
--- a/src/backend/utils/misc/guc-file.l
+++ b/src/backend/utils/misc/guc-file.l
@@ -567,6 +567,22 @@ ParseConfigFile(const char *config_file, bool strict,
 	bool		OK = true;
 	FILE	   *fp;
 
+	/*
+	 * Reject file name that is all-blank (including empty), as that leads to
+	 * confusion --- we'd try to read the containing directory as a file.
+	 */
+	if (strspn(config_file, " \t\r\n") == strlen(config_file))
+	{
+		ereport(elevel,
+				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+				 errmsg("empty configuration file name: \"%s\"",
+						config_file)));
+		record_config_file_error("empty configuration file name",
+								 calling_file, calling_lineno,
+								 head_p, tail_p);
+		return false;
+	}
+
 	/*
 	 * Reject too-deep include nesting depth.  This is just a safety check to
 	 * avoid dumping core due to stack overflow if an include file loops back
@@ -585,6 +601,26 @@ ParseConfigFile(const char *config_file, bool strict,
 	}
 
 	abs_path = AbsoluteConfigLocation(config_file, calling_file);
+
+	/*
+	 * Reject direct recursion.  Indirect recursion is also possible, but it's
+	 * harder to detect and so doesn't seem worth the trouble.  (We test at
+	 * this step because the canonicalization done by AbsoluteConfigLocation
+	 * makes it more likely that a simple strcmp comparison will match.)
+	 */
+	if (calling_file && strcmp(abs_path, calling_file) == 0)
+	{
+		ereport(elevel,
+				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+				 errmsg("configuration file recursion in \"%s\"",
+						calling_file)));
+		record_config_file_error("configuration file recursion",
+								 calling_file, calling_lineno,
+								 head_p, tail_p);
+		pfree(abs_path);
+		return false;
+	}
+
 	fp = AllocateFile(abs_path, "r");
 	if (!fp)
 	{
@@ -933,6 +969,28 @@ ParseConfigDirectory(const char *includedir,
 	int			size_filenames;
 	bool		status;
 
+	/*
+	 * Reject directory name that is all-blank (including empty), as that
+	 * leads to confusion --- we'd read the containing directory, typically
+	 * resulting in recursive inclusion of the same file(s).
+	 */
+	if (strspn(includedir, " \t\r\n") == strlen(includedir))
+	{
+		ereport(elevel,
+				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+				 errmsg("empty configuration directory name: \"%s\"",
+						includedir)));
+		record_config_file_error("empty configuration directory name",
+								 calling_file, calling_lineno,
+								 head_p, tail_p);
+		return false;
+	}
+
+	/*
+	 * We don't check for recursion or too-deep nesting depth here; the
+	 * subsequent calls to ParseConfigFile will take care of that.
+	 */
+
 	directory = AbsoluteConfigLocation(includedir, calling_file);
 	d = AllocateDir(directory);
 	if (d == NULL)
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index 179869f1d9c..41191d4f457 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -675,12 +675,13 @@
 #------------------------------------------------------------------------------
 
 # These options allow settings to be loaded from files other than the
-# default postgresql.conf.
+# default postgresql.conf.  Note that these are directives, not variable
+# assignments, so they can usefully be given more than once.
 
-#include_dir = ''			# include files ending in '.conf' from
+#include_dir = '...'			# include files ending in '.conf' from
 					# a directory, e.g., 'conf.d'
-#include_if_exists = ''			# include file only if it exists
-#include = ''				# include file
+#include_if_exists = '...'		# include file only if it exists
+#include = '...'			# include file
 
 
 #------------------------------------------------------------------------------