diff --git a/src/calibre/gui2/pictureflow/pictureflow.cpp b/src/calibre/gui2/pictureflow/pictureflow.cpp
index 9b0e094ee4..9fe3301fbe 100644
--- a/src/calibre/gui2/pictureflow/pictureflow.cpp
+++ b/src/calibre/gui2/pictureflow/pictureflow.cpp
@@ -587,7 +587,7 @@ void PictureFlowPrivate::resetSlides()
   {
     SlideInfo& si = leftSlides[i];
     si.angle = itilt;
-    si.cx = -(offsetX + spacing*i*PFREAL_ONE);
+    si.cx = -(offsetX + (long)spacing*i*PFREAL_ONE);
     si.cy = offsetY;
     si.slideIndex = centerIndex-1-i;
     //qDebug() << "Left[" << i << "] x=" << fixedToFloat(si.cx) << ", y=" << fixedToFloat(si.cy) ;
@@ -599,7 +599,7 @@ void PictureFlowPrivate::resetSlides()
   {
     SlideInfo& si = rightSlides[i];
     si.angle = -itilt;
-    si.cx = offsetX + spacing*i*PFREAL_ONE;
+    si.cx = offsetX + (long)spacing*i*PFREAL_ONE;
     si.cy = offsetY;
     si.slideIndex = centerIndex+1+i;
     //qDebug() << "Right[" << i << "] x=" << fixedToFloat(si.cx) << ", y=" << fixedToFloat(si.cy) ;
@@ -1118,7 +1118,7 @@ void PictureFlowPrivate::updateAnimation()
     speed = 512 + 16384 * (PFREAL_ONE+fsin(ia))/PFREAL_ONE;
   }
 
-  slideFrame += speed*step;
+  slideFrame += (long long)speed*step;
 
   int index = slideFrame >> 16;
   int pos = slideFrame & 0xffff;
@@ -1161,7 +1161,7 @@ void PictureFlowPrivate::updateAnimation()
   {
     SlideInfo& si = leftSlides[i];
     si.angle = itilt;
-    si.cx = -(offsetX + spacing*i*PFREAL_ONE + step*spacing*ftick);
+    si.cx = -(offsetX + (long)spacing*i*PFREAL_ONE + (long)step*spacing*ftick);
     si.cy = offsetY;
   }
 
@@ -1169,7 +1169,7 @@ void PictureFlowPrivate::updateAnimation()
   {
     SlideInfo& si = rightSlides[i];
     si.angle = -itilt;
-    si.cx = offsetX + spacing*i*PFREAL_ONE - step*spacing*ftick;
+    si.cx = offsetX + (long)spacing*i*PFREAL_ONE - (long)step*spacing*ftick;
     si.cy = offsetY;
   }
 
diff --git a/src/calibre/utils/ffmpeg.c b/src/calibre/utils/ffmpeg.c
index 616eab94e4..db9091f40a 100644
--- a/src/calibre/utils/ffmpeg.c
+++ b/src/calibre/utils/ffmpeg.c
@@ -510,7 +510,7 @@ resample_raw_audio_16bit(PyObject *self, PyObject *args) {
     );
     Py_END_ALLOW_THREADS
     if (ret < 0) { free_resources; return averror_as_python_with_gil_held(ret, __LINE__); }
-    output_size = ret * output_num_channels * bytes_per_sample;
+    output_size = (int64_t)ret * (int64_t)output_num_channels * bytes_per_sample;
     PyObject *ans = PyBytes_FromStringAndSize((char*)output, output_size);
     free_resources;
 #undef free_resources
diff --git a/src/calibre/utils/imageops/imageops.cpp b/src/calibre/utils/imageops/imageops.cpp
index 2330fb4196..7524f6dcc0 100644
--- a/src/calibre/utils/imageops/imageops.cpp
+++ b/src/calibre/utils/imageops/imageops.cpp
@@ -174,7 +174,7 @@ static QImage convolve(const QImage &image, int matrix_size, float *matrix) {
     if (buffer.isNull()) throw std::bad_alloc();
     buf1.resize(matrix_size);
     scanblock = buf1.data();
-    buf2.resize(matrix_size * matrix_size);
+    buf2.resize((qsizetype)matrix_size * matrix_size);
     normalize_matrix = buf2.data();
 
     // create normalized matrix
diff --git a/src/calibre/utils/lzx/lzxc.c b/src/calibre/utils/lzx/lzxc.c
index 4014224b5e..f0d5c8152d 100644
--- a/src/calibre/utils/lzx/lzxc.c
+++ b/src/calibre/utils/lzx/lzxc.c
@@ -18,7 +18,6 @@
 #define LZ_ONEBUFFER 1
 #define LAZY 1
 
-#include <stdio.h>
 #include <stdlib.h>
 #include <stdint.h>
 #include <string.h> /* for memset on Linux */
@@ -1143,7 +1142,7 @@ int lzxc_compress_block(lzxc_data *lzxd, int block_size, int subdivide)
       build_huffman_tree(LZX_ALIGNED_SIZE, 7, lzxd->aligned_freq_table, lzxd->aligned_tree);
       for (i = 0; i < LZX_ALIGNED_SIZE; i++) {
 	uncomp_bits += lzxd->aligned_freq_table[i]* 3;
-	comp_bits += lzxd->aligned_freq_table[i]* lzxd->aligned_tree[i].codelength;
+	comp_bits += (long)lzxd->aligned_freq_table[i]* lzxd->aligned_tree[i].codelength;
       }
       comp_bits_ovh = comp_bits + LZX_ALIGNED_SIZE * 3;
       if (comp_bits_ovh < uncomp_bits)
diff --git a/src/calibre/utils/lzx/lzxd.c b/src/calibre/utils/lzx/lzxd.c
index b416a9b6ed..67d6aecbbf 100644
--- a/src/calibre/utils/lzx/lzxd.c
+++ b/src/calibre/utils/lzx/lzxd.c
@@ -224,8 +224,8 @@ static int make_decode_table(unsigned int nsyms, unsigned int nbits,
   unsigned int next_symbol = bit_mask; /* base of allocation for long codes */
 
   /* fill entries for codes short enough for a direct mapping */
-  for (bit_num = 1; bit_num <= nbits; bit_num++) {
-    for (sym = 0; sym < nsyms; sym++) {
+  for (bit_num = 1; (unsigned)bit_num <= nbits; bit_num++) {
+    for (sym = 0; (unsigned)sym < nsyms; sym++) {
       if (length[sym] != bit_num) continue;
       leaf = pos;
       if((pos += bit_mask) > table_mask) return 1; /* table overrun */
@@ -239,7 +239,7 @@ static int make_decode_table(unsigned int nsyms, unsigned int nbits,
   if (pos == table_mask) return 0;
 
   /* clear the remainder of the table */
-  for (sym = pos; sym < table_mask; sym++) table[sym] = 0xFFFF;
+  for (sym = pos; (unsigned)sym < table_mask; sym++) table[sym] = 0xFFFF;
 
   /* allow codes to be up to nbits+16 long, instead of nbits */
   pos <<= 16;
@@ -247,7 +247,7 @@ static int make_decode_table(unsigned int nsyms, unsigned int nbits,
   bit_mask = 1 << 15;
 
   for (bit_num = nbits+1; bit_num <= 16; bit_num++) {
-    for (sym = 0; sym < nsyms; sym++) {
+    for (sym = 0; (unsigned)sym < nsyms; sym++) {
       if (length[sym] != bit_num) continue;
 
       leaf = pos >> 16;
@@ -273,7 +273,7 @@ static int make_decode_table(unsigned int nsyms, unsigned int nbits,
   if (pos == table_mask) return 0;
 
   /* either erroneous table, or all elements are 0 - let's find out. */
-  for (sym = 0; sym < nsyms; sym++) if (length[sym]) return 1;
+  for (sym = 0; (unsigned)sym < nsyms; sym++) if (length[sym]) return 1;
   return 0;
 }
 
diff --git a/src/calibre/utils/matcher.c b/src/calibre/utils/matcher.c
index af19fad158..77a87aa6a1 100644
--- a/src/calibre/utils/matcher.c
+++ b/src/calibre/utils/matcher.c
@@ -27,7 +27,7 @@ typedef struct {
 
 static MemoryItem*** alloc_memory(int32_t needle_len, int32_t max_haystack_len) {
     MemoryItem ***ans = NULL, **d1 = NULL, *d2 = NULL;
-    size_t num = max_haystack_len * max_haystack_len * needle_len;
+    size_t num = (size_t)max_haystack_len * (size_t)max_haystack_len * needle_len;
     size_t position_sz = needle_len * sizeof(int32_t);
     size_t sz = (num * (sizeof(MemoryItem) + position_sz)) + (max_haystack_len * sizeof(MemoryItem**)) + (needle_len * sizeof(MemoryItem*));
     int32_t hidx, nidx, last_idx, i, j;
@@ -85,7 +85,7 @@ typedef struct {
 static void alloc_stack(Stack *stack, int32_t needle_len, int32_t max_haystack_len) {
     StackItem *ans = NULL;
     char *base = NULL;
-    size_t num = max_haystack_len * needle_len;
+    size_t num = (size_t)max_haystack_len * needle_len;
     size_t position_sz = needle_len * sizeof(int32_t);
     size_t sz = sizeof(StackItem) + position_sz;
     size_t i = 0;
@@ -416,7 +416,7 @@ Matcher_calculate_scores(Matcher *self, PyObject *args) {
     items = PyTuple_New(self->item_count);
     positions = PyTuple_New(self->item_count);
     matches = (Match*)calloc(self->item_count, sizeof(Match));
-    final_positions = (int32_t*) calloc(needle_char_len * self->item_count, sizeof(int32_t));
+    final_positions = (int32_t*) calloc((size_t)needle_char_len * self->item_count, sizeof(int32_t));
     if (items == NULL || matches == NULL || final_positions == NULL || positions == NULL) {PyErr_NoMemory(); goto end;}
 
     for (i = 0; i < self->item_count; i++) {