diff --git a/src/config.c b/src/config.c
index 7bf83095..2800ed0f 100644
--- a/src/config.c
+++ b/src/config.c
@@ -352,6 +352,7 @@ TOKEN *new_constant(const char *con) {
     !strcmp("HAS_VTARG_SWITCH", con)? HAS_VTARG_SWITCH:
     !strcmp("HAS_VTARG_ADJ", con)? HAS_VTARG_ADJ:
     !strcmp("HAS_VTARG_READ", con)? HAS_VTARG_READ:
+    !strcmp("HAS_FOSC_ADJ", con)? HAS_FOSC_ADJ:
     !strcmp("pseudo", con)? 2:
     !strcmp("yes", con) || !strcmp("true", con)? 1:
     !strcmp("no", con) || !strcmp("false", con)? 0:
diff --git a/src/developer_opts.c b/src/developer_opts.c
index 83070ea5..1db1d38d 100644
--- a/src/developer_opts.c
+++ b/src/developer_opts.c
@@ -256,6 +256,8 @@ static char *extra_features_str(int m) {
     strcat(mode, " | HAS_VTARG_ADJ");
   if(m & HAS_VTARG_READ)
     strcat(mode, " | HAS_VTARG_READ");
+  if(m & HAS_FOSC_ADJ)
+    strcat(mode, " | HAS_FOSC_ADJ");
 
   return mode + (mode[1] == 0? 0: 4);
 }
diff --git a/src/lexer.l b/src/lexer.l
index 5a568ae6..ac0e7db2 100644
--- a/src/lexer.l
+++ b/src/lexer.l
@@ -145,7 +145,7 @@ SIGN     [+-]
 
 
 (?x: PM_(SPM|TPI|ISP|PDI|UPDI|HVSP|HVPP|debugWIRE|JTAG|JTAGmkI|XMEGAJTAG|AVR32JTAG|aWire) |
- HAS_(SUFFER|VTARG_SWITCH|VTARG_ADJ|VTARG_READ) |
+ HAS_(SUFFER|VTARG_SWITCH|VTARG_ADJ|VTARG_READ|FOSC_ADJ) |
  yes|no|pseudo | true|false ) { /* Constants */
   yylval = new_constant(yytext);
   return TKN_NUMBER;
diff --git a/src/libavrdude.h b/src/libavrdude.h
index 01105bc0..1ef6381f 100644
--- a/src/libavrdude.h
+++ b/src/libavrdude.h
@@ -215,6 +215,7 @@ typedef struct opcode {
 #define HAS_VTARG_SWITCH       2
 #define HAS_VTARG_ADJ          4
 #define HAS_VTARG_READ         8
+#define HAS_FOSC_ADJ          16
 
 #define AVR_FAMILYIDLEN 7
 #define AVR_SIBLEN 16