diff --git a/include/psyc/text.h b/include/psyc/text.h
index 03d7aff..0588b65 100644
--- a/include/psyc/text.h
+++ b/include/psyc/text.h
@@ -62,8 +62,8 @@ typedef struct {
  * PSYC_TEXT_VALUE_NOT_FOUND if no match found in which case psyc_text
  * leaves the original template text as is.
  */
-typedef PsycTextValueRC (*PsycTextCB) (const char *name, size_t len,
-				       PsycString *value, void *extra);
+typedef PsycTextValueRC (*PsycTextCB) (void *cls, const char *name, size_t namelen,
+				       PsycString *value);
 
 /**
  * Initializes the PSYC text state struct.
@@ -156,7 +156,7 @@ psyc_text_bytes_written (PsycTextState *state)
  * @see http://about.psyc.eu/psyctext
  **/
 PsycTextRC
-psyc_text (PsycTextState *state, PsycTextCB getValue, void *extra);
+psyc_text (PsycTextState *state, PsycTextCB get_value, void *get_value_cls);
 
 extern const PsycTemplates psyc_templates;
 
diff --git a/src/render.c b/src/render.c
index f0a93fe..d61e68e 100644
--- a/src/render.c
+++ b/src/render.c
@@ -60,7 +60,7 @@ psyc_render_table (PsycTable *table, char *buffer, size_t buflen)
 }
 
 static inline size_t
-psyc_render_modifier (PsycModifier * mod, char *buffer)
+psyc_render_modifier (PsycModifier *mod, char *buffer)
 {
     size_t cur = 0;
 
@@ -87,7 +87,7 @@ psyc_render_modifier (PsycModifier * mod, char *buffer)
 static inline
 #endif
 PsycRenderRC
-psyc_render (PsycPacket * packet, char *buffer, size_t buflen)
+psyc_render (PsycPacket *packet, char *buffer, size_t buflen)
 {
     size_t i, cur = 0, len;
 
diff --git a/src/text.c b/src/text.c
index 6c91446..390460d 100644
--- a/src/text.c
+++ b/src/text.c
@@ -6,7 +6,7 @@ const PsycTemplates psyc_templates = { .s = {
 }};
 
 PsycTextRC
-psyc_text (PsycTextState *state, PsycTextCB get_value, void *extra)
+psyc_text (PsycTextState *state, PsycTextCB get_value, void *get_value_cls)
 {
     const char *start = state->tmpl.data, *end; // start & end of variable name
     const char *prev = state->tmpl.data + state->cursor;
@@ -38,8 +38,8 @@ psyc_text (PsycTextState *state, PsycTextCB get_value, void *extra)
 	    continue; // [] is invalid, name can't be empty
 	}
 
-	ret = get_value(start + state->open.length,
-		       end - start - state->open.length, &value, extra);
+	ret = get_value(get_value_cls, start + state->open.length,
+			end - start - state->open.length, &value);
 
 	if (ret < 0)
 	    continue; // value not found, no substitution
diff --git a/test/test_text.c b/test/test_text.c
index 977a66e..cd6bf46 100644
--- a/test/test_text.c
+++ b/test/test_text.c
@@ -8,7 +8,7 @@
 uint8_t verbose;
 
 PsycTextValueRC
-getValueFooBar (const char *name, size_t len, PsycString *value, void *extra)
+getValueFooBar (void *cls, const char *name, size_t len, PsycString *value)
 {
     if (verbose)
 	printf("> getValue: %.*s\n", (int)len, name);
@@ -18,7 +18,7 @@ getValueFooBar (const char *name, size_t len, PsycString *value, void *extra)
 }
 
 PsycTextValueRC
-getValueEmpty (const char *name, size_t len, PsycString *value, void *extra)
+getValueEmpty (void *cls, const char *name, size_t len, PsycString *value)
 {
     if (verbose)
 	printf("> getValue: %.*s\n", (int)len, name);
@@ -28,7 +28,7 @@ getValueEmpty (const char *name, size_t len, PsycString *value, void *extra)
 }
 
 PsycTextValueRC
-getValueNotFound (const char *name, size_t len, PsycString *value, void *extra)
+getValueNotFound (void *cls, const char *name, size_t len, PsycString *value)
 {
     if (verbose)
 	printf("> getValue: %.*s\n", (int)len, name);