diff --git a/spacy/tokens/doc.pxd b/spacy/tokens/doc.pxd
index d5435ed00..aa2cf6b54 100644
--- a/spacy/tokens/doc.pxd
+++ b/spacy/tokens/doc.pxd
@@ -46,4 +46,4 @@ cdef class Doc:
 
     cpdef np.ndarray to_array(self, object features)
 
-    cdef int set_parse(self, const TokenC* parsed) except -1
+    cdef void set_parse(self, const TokenC* parsed) nogil
diff --git a/spacy/tokens/doc.pyx b/spacy/tokens/doc.pyx
index 1845a5562..50f4a2021 100644
--- a/spacy/tokens/doc.pyx
+++ b/spacy/tokens/doc.pyx
@@ -373,7 +373,7 @@ cdef class Doc:
         for i in range(self.length, self.max_length + PADDING):
             self.c[i].lex = &EMPTY_LEXEME
 
-    cdef int set_parse(self, const TokenC* parsed) except -1:
+    cdef void set_parse(self, const TokenC* parsed) nogil:
         # TODO: This method is fairly misleading atm. It's used by Parser
         # to actually apply the parse calculated. Need to rethink this.
 
@@ -381,8 +381,6 @@ cdef class Doc:
         self.is_parsed = True
         for i in range(self.length):
             self.c[i] = parsed[i]
-            assert self.c[i].l_edge <= i
-            assert self.c[i].r_edge >= i
 
     def from_array(self, attrs, array):
         cdef int i, col