diff --git a/contrib/tsearch2/ispell/spell.c b/contrib/tsearch2/ispell/spell.c
index 7fb720f582c..9027263a18d 100644
--- a/contrib/tsearch2/ispell/spell.c
+++ b/contrib/tsearch2/ispell/spell.c
@@ -463,9 +463,9 @@ mkSPNode(IspellDict * Conf, int low, int high, int level)
 	if (!nchar)
 		return NULL;
 
-	rs = (SPNode *) malloc(SPNHRDSZ + nchar * sizeof(SPNodeData));
+	rs = (SPNode *) malloc(SPNHDRSZ + nchar * sizeof(SPNodeData));
 	MEMOUT(rs);
-	memset(rs, 0, SPNHRDSZ + nchar * sizeof(SPNodeData));
+	memset(rs, 0, SPNHDRSZ + nchar * sizeof(SPNodeData));
 	rs->length = nchar;
 	data = rs->data;
 
diff --git a/contrib/tsearch2/ispell/spell.h b/contrib/tsearch2/ispell/spell.h
index ee86eac9856..549bb68091f 100644
--- a/contrib/tsearch2/ispell/spell.h
+++ b/contrib/tsearch2/ispell/spell.h
@@ -27,7 +27,7 @@ typedef struct SPNode
 	SPNodeData	data[1];
 }	SPNode;
 
-#define SPNHRDSZ	(sizeof(uint32))
+#define SPNHDRSZ	(offsetof(SPNode,data))
 
 
 typedef struct spell_struct
@@ -89,7 +89,7 @@ typedef struct AffixNode
 	AffixNodeData data[1];
 }	AffixNode;
 
-#define ANHRDSZ		   (sizeof(uint32))
+#define ANHRDSZ		   (offsetof(AffixNode, data))
 
 typedef struct
 {