diff --git a/doc/src/sgml/libpq.sgml b/doc/src/sgml/libpq.sgml
index be0d602..0bac166 100644
--- a/doc/src/sgml/libpq.sgml
+++ b/doc/src/sgml/libpq.sgml
@@ -136,10 +136,11 @@ PGconn *PQconnectdbParams(const char * const *keywords,
       </para>
 
       <para>
-       If  any  parameter is unspecified, then the corresponding
-       environment variable (see <xref linkend="libpq-envars">)
-       is checked. If the  environment  variable is not set either,
-       then the indicated built-in defaults are used.
+       If  any  parameter is unspecified, then the corresponding environment
+       variable (see <xref linkend="libpq-envars">) is checked. Parameters are
+       treated as unspecified if they are either NULL or contain an empty string
+       ("").  If the  environment  variable is not set either, then the
+       indicated built-in defaults are used.
       </para>
 
       <para>
diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c
index d53c41f..253615e 100644
--- a/src/interfaces/libpq/fe-connect.c
+++ b/src/interfaces/libpq/fe-connect.c
@@ -4321,7 +4321,7 @@ conninfo_array_parse(const char *const * keywords, const char *const * values,
 		const char *pname = keywords[i];
 		const char *pvalue = values[i];
 
-		if (pvalue != NULL)
+		if (pvalue != NULL && pvalue[0] != '\0')
 		{
 			/* Search for the param record */
 			for (option = options; option->keyword != NULL; option++)