diff --git a/backend/ma1509.c b/backend/ma1509.c
index 472269005..3c6a6bb9a 100644
--- a/backend/ma1509.c
+++ b/backend/ma1509.c
@@ -48,7 +48,7 @@
 
 /**************************************************************************/
 /* ma1509 backend version                                                 */
-#define BUILD 2
+#define BUILD 3
 /**************************************************************************/
 
 #include "../include/sane/config.h"
@@ -1165,6 +1165,12 @@ sane_init (SANE_Int * version_code, SANE_Auth_Callback authorize)
 	  word = 0;
 	  cp = sanei_config_get_string (cp, &word);
 
+	  if (!word)
+	    {
+	      DBG (1, "sane_init: config file line %d: missing quotation mark?\n",
+		   linenumber);
+	      continue;
+	    }
 
 	  if (strcmp (word, "warmup-time") == 0)
 	    {
@@ -1173,6 +1179,14 @@ sane_init (SANE_Int * version_code, SANE_Auth_Callback authorize)
 	      free (word);
 	      word = 0;
 	      cp = sanei_config_get_string (cp, &word);
+
+	      if (!word)
+		{
+		  DBG (1, "sane_init: config file line %d: missing quotation mark?\n",
+		       linenumber);
+		  continue;
+		}
+
 	      errno = 0;
 	      local_warmup_time = strtol (word, &end, 0);
 
diff --git a/backend/mustek.c b/backend/mustek.c
index 3af0a9188..1af2715cf 100644
--- a/backend/mustek.c
+++ b/backend/mustek.c
@@ -46,7 +46,7 @@
 
 /**************************************************************************/
 /* Mustek backend version                                                 */
-#define BUILD 132
+#define BUILD 133
 /**************************************************************************/
 
 #include "../include/sane/config.h"
@@ -5112,12 +5112,25 @@ sane_init (SANE_Int * version_code, SANE_Auth_Callback authorize)
 	  free (word);
 	  word = 0;
 	  cp = sanei_config_get_string (cp, &word);
+	  if (!word)
+	    {
+	      DBG (1, "sane_init: config file line %d: missing quotation mark?\n",
+		   linenumber);
+	      continue;
+	    }
 
 	  if (strcmp (word, "strip-height") == 0)
 	    {
 	      free (word);
 	      word = 0;
 	      cp = sanei_config_get_string (cp, &word);
+	      if (!word)
+		{
+		  DBG (1, "sane_init: config file line %d: missing quotation mark?\n",
+		       linenumber);
+		  continue;
+		}
+
 	      errno = 0;
 	      strip_height = strtod (word, &end);
 	      if (end == word)
@@ -5264,6 +5277,13 @@ sane_init (SANE_Int * version_code, SANE_Auth_Callback authorize)
 	      free (word);
 	      word = 0;
 	      cp = sanei_config_get_string (cp, &word);
+	      if (!word)
+		{
+		  DBG (1, "sane_init: config file line %d: missing quotation mark?\n",
+		       linenumber);
+		  continue;
+		}
+
 	      errno = 0;
 	      buffer_size = strtol (word, &end, 0);
 
@@ -5311,6 +5331,13 @@ sane_init (SANE_Int * version_code, SANE_Auth_Callback authorize)
 	      free (word);
 	      word = 0;
 	      cp = sanei_config_get_string (cp, &word);
+	      if (!word)
+		{
+		  DBG (1, "sane_init: config file line %d: missing quotation mark?\n",
+		       linenumber);
+		  continue;
+		}
+
 	      errno = 0;
 	      block_size = strtol (word, &end, 0);
 
diff --git a/backend/mustek_usb.c b/backend/mustek_usb.c
index afa20023c..5344e6b93 100644
--- a/backend/mustek_usb.c
+++ b/backend/mustek_usb.c
@@ -46,7 +46,7 @@
    This file implements a SANE backend for Mustek 1200UB and similar 
    USB flatbed scanners.  */
 
-#define BUILD 16
+#define BUILD 17
 
 #include "../include/sane/config.h"
 
@@ -764,11 +764,25 @@ sane_init (SANE_Int * version_code, SANE_Auth_Callback authorize)
 	  word = 0;
 	  cp = sanei_config_get_string (cp, &word);
 
+	  if (!word)
+	    {
+	      DBG (1, "sane_init: config file line %d: missing quotation mark?\n",
+		   linenumber);
+	      continue;
+	    }
+
 	  if (strcmp (word, "max_block_size") == 0)
 	    {
 	      free (word);
 	      word = 0;
 	      cp = sanei_config_get_string (cp, &word);
+	      if (!word)
+		{
+		  DBG (1, "sane_init: config file line %d: missing quotation mark?\n",
+		       linenumber);
+		  continue;
+		}
+
 	      errno = 0;
 	      max_block_size = strtol (word, &end, 0);
 	      if (end == word)
diff --git a/backend/test.c b/backend/test.c
index 61de5bfe6..b6084b1d8 100644
--- a/backend/test.c
+++ b/backend/test.c
@@ -41,7 +41,7 @@
    This backend is for testing frontends.
 */
 
-#define BUILD 21
+#define BUILD 22
 
 #include "../include/sane/config.h"
 
@@ -1088,6 +1088,9 @@ read_option (SANE_String line, SANE_String option_string,
 
   cp = sanei_config_get_string (line, &word);
 
+  if (!word)
+    return SANE_STATUS_INVAL;
+
   if (strcmp (word, option_string) != 0)
     return SANE_STATUS_INVAL;
 
@@ -1101,6 +1104,8 @@ read_option (SANE_String line, SANE_String option_string,
     case param_bool:
       {
 	cp = sanei_config_get_string (cp, &word);
+	if (!word)
+	  return SANE_STATUS_INVAL;
 	if (strlen (word) == 0)
 	  {
 	    DBG (3, "read_option: option `%s' requires parameter\n",
@@ -1126,6 +1131,8 @@ read_option (SANE_String line, SANE_String option_string,
 	SANE_Int int_value;
 
 	cp = sanei_config_get_string (cp, &word);
+	if (!word)
+	  return SANE_STATUS_INVAL;
 	errno = 0;
 	int_value = (SANE_Int) strtol (word, &end, 0);
 	if (end == word)
@@ -1154,6 +1161,8 @@ read_option (SANE_String line, SANE_String option_string,
 	SANE_Fixed fixed_value;
 
 	cp = sanei_config_get_string (cp, &word);
+	if (!word)
+	  return SANE_STATUS_INVAL;
 	errno = 0;
 	double_value = strtod (word, &end);
 	if (end == word)
@@ -1180,6 +1189,8 @@ read_option (SANE_String line, SANE_String option_string,
     case param_string:
       {
 	cp = sanei_config_get_string (cp, &word);
+	if (!word)
+	  return SANE_STATUS_INVAL;
 	if (strlen (word) == 0)
 	  {
 	    DBG (3, "read_option: option `%s' requires parameter\n",