diff --git a/ggml-metal.metal b/ggml-metal.metal
index cfcc32257..aa954926b 100644
--- a/ggml-metal.metal
+++ b/ggml-metal.metal
@@ -2526,12 +2526,17 @@ typedef struct {
 // 98 bytes / block for QK_K = 256, so 3.0625 bpw
 
 // 3.4375 bpw
+#if QK_K == 64
+#define IQ3S_N_SCALE 2
+#else
+#define IQ3S_N_SCALE QK_K/64
+#endif
 typedef struct {
     half d;
     uint8_t qs[QK_K/4];
     uint8_t qh[QK_K/32];
     uint8_t signs[QK_K/8];
-    uint8_t scales[QK_K/64];
+    uint8_t scales[IQ3S_N_SCALE];
 } block_iq3_s;
 
 typedef struct {
diff --git a/ggml-quants.c b/ggml-quants.c
index c1a168328..5c5f2ce1b 100644
--- a/ggml-quants.c
+++ b/ggml-quants.c
@@ -10772,7 +10772,7 @@ static void quantize_row_iq3_xxs_impl(int grid_size, const float * restrict x, v
 
     const int kMaxQ = 8;
 
-    const int nbl = n/256;
+    const int nbl = n/QK_K;
 
     ggml_fp16_t * dh;
     uint8_t * qs;
@@ -11018,7 +11018,7 @@ static void quantize_row_iq3_s_impl(int block_size, const float * restrict x, vo
 
     const int kMaxQ = 8;
 
-    const int nbl = n/256;
+    const int nbl = n/QK_K;
 
     block_iq3_s * y = vy;
 
@@ -11189,7 +11189,7 @@ size_t quantize_iq3_s(const float * src, void * dst, int nrow, int n_per_row, in
     uint8_t block_signs[IQ3S_BLOCK_SIZE/8];
     char * qrow = (char *)dst;
     for (int row = 0; row < nrow; ++row) {
-        quantize_row_iq3_s_impl(32, src, qrow, n_per_row, quant_weights,
+        quantize_row_iq3_s_impl(IQ3S_BLOCK_SIZE, src, qrow, n_per_row, quant_weights,
                 scales, weight, xval, L, Laux, waux, is_on_grid, is_on_grid_aux, block_signs);
         src += n_per_row;
         qrow += nblock*sizeof(block_iq3_s);
diff --git a/ggml-quants.h b/ggml-quants.h
index c217db925..303b0b6f9 100644
--- a/ggml-quants.h
+++ b/ggml-quants.h
@@ -191,15 +191,20 @@ typedef struct {
 } block_iq3_xxs;
 static_assert(sizeof(block_iq3_xxs) == sizeof(ggml_fp16_t) + 3*(QK_K/8), "wrong iq3_xxs block size/padding");
 
-// 3.3125 bpw
+// 3.4375 bpw
+#if QK_K == 64
+#define IQ3S_N_SCALE 2
+#else
+#define IQ3S_N_SCALE QK_K/64
+#endif
 typedef struct {
     ggml_fp16_t d;
     uint8_t qs[QK_K/4];
     uint8_t qh[QK_K/32];
     uint8_t signs[QK_K/8];
-    uint8_t scales[QK_K/64];
+    uint8_t scales[IQ3S_N_SCALE];
 } block_iq3_s;
-static_assert(sizeof(block_iq3_s) == sizeof(ggml_fp16_t) + 27*(QK_K/64), "wrong iq3_s block size/padding");
+static_assert(sizeof(block_iq3_s) == sizeof(ggml_fp16_t) + 13*(QK_K/32) + IQ3S_N_SCALE, "wrong iq3_s block size/padding");
 
 typedef struct {
     ggml_fp16_t d;