diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 625f9a86..5f204107 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -192,7 +192,7 @@ jobs:
     - name: test-all
       if: always()
       run: |
-        make clean test-all
+        make clean test-all MOREFLAGS="-Wconversion -Werror"
 
     - name: test-alias
       run: |
@@ -237,7 +237,6 @@ jobs:
     - name: tests/bench
       run: |
         make -C tests/bench
-        make -C tests/bench clean main.o CC=gcc MOREFLAGS="-Wconversion -Werror"
 
 
   ubuntu-wasm:
diff --git a/cli/xsum_os_specific.c b/cli/xsum_os_specific.c
index 8438d0cf..ab86bb41 100644
--- a/cli/xsum_os_specific.c
+++ b/cli/xsum_os_specific.c
@@ -186,6 +186,7 @@ static wchar_t* XSUM_widenString(const char* str, int* lenOut)
  * Converts a UTF-16 string to UTF-8. Acts like strdup. The string must be freed afterwards.
  * This version allows keeping the output length.
  */
+#ifndef XSUM_NO_MAIN
 static char* XSUM_narrowString(const wchar_t *str, int *lenOut)
 {
     int len = WideCharToMultiByte(CP_UTF8, 0, str, -1, NULL, 0, NULL, NULL);
@@ -200,6 +201,7 @@ static char* XSUM_narrowString(const wchar_t *str, int *lenOut)
         return buf;
     }
 }
+#endif
 
 
 
diff --git a/tests/Makefile b/tests/Makefile
index ee2e5fc9..1c8a936e 100644
--- a/tests/Makefile
+++ b/tests/Makefile
@@ -24,7 +24,7 @@
 # ################################################################
 
 MAKEFLAGS += --no-print-directory
-CFLAGS += -Wall -Wextra -Wundef -g
+CFLAGS += -Wall -Wextra -Wundef -g $(MOREFLAGS)
 
 CP = cp
 NM = nm
diff --git a/tests/bench/benchHash.c b/tests/bench/benchHash.c
index 5da4678e..cd3693c6 100644
--- a/tests/bench/benchHash.c
+++ b/tests/bench/benchHash.c
@@ -115,7 +115,7 @@ bench_hash_internal(BMK_benchFn_t hashfn, void* payload,
 
     free(srcBuffer);
     assert(runTime.nanoSecPerRun != 0);
-    return (1000000000U / runTime.nanoSecPerRun) * nbBlocks;
+    return (1000000000U / runTime.nanoSecPerRun) * (double)nbBlocks;
 
 }
 
diff --git a/tests/bench/benchfn.c b/tests/bench/benchfn.c
index 9d8f7265..fbd149d2 100644
--- a/tests/bench/benchfn.c
+++ b/tests/bench/benchfn.c
@@ -226,9 +226,9 @@ BMK_runOutcome_t BMK_benchTimedFn(BMK_timedFnState_t* cont,
             cont->timeSpent_ns += (unsigned long long)loopDuration_ns;
 
             /* estimate nbLoops for next run to last approximately 1 second */
-            if (loopDuration_ns > (runBudget_ns / 50)) {
+            if (loopDuration_ns > (double)(runBudget_ns / 50)) {
                 double const fastestRun_ns = MIN(bestRunTime.nanoSecPerRun, newRunTime.nanoSecPerRun);
-                cont->nbLoops = (unsigned)(runBudget_ns / fastestRun_ns) + 1;
+                cont->nbLoops = (unsigned)((double)runBudget_ns / fastestRun_ns) + 1;
             } else {
                 /* previous run was too short : blindly increase workload by x multiplier */
                 const unsigned multiplier = 10;
@@ -236,7 +236,7 @@ BMK_runOutcome_t BMK_benchTimedFn(BMK_timedFnState_t* cont,
                 cont->nbLoops *= multiplier;
             }
 
-            if (loopDuration_ns < runTimeMin_ns) {
+            if (loopDuration_ns < (double)runTimeMin_ns) {
                 /* When benchmark run time is too small : don't report results.
                  * increased risks of rounding errors */
                 continue;
diff --git a/tests/bench/bhDisplay.c b/tests/bench/bhDisplay.c
index eb9c197e..ee8ed4f6 100644
--- a/tests/bench/bhDisplay.c
+++ b/tests/bench/bhDisplay.c
@@ -48,7 +48,7 @@ static void bench_oneHash_largeInput(Bench_Entry hashDesc, int minlog, int maxlo
         double const nbhps = bench_hash(hashDesc.hash, BMK_throughput,
                                         inputSize, BMK_fixedSize,
                                         BENCH_LARGE_TOTAL_MS, BENCH_LARGE_ITER_MS);
-        printf(",%6.0f", nbhps * inputSize / MB_UNIT); fflush(NULL);
+        printf(",%6.0f", nbhps * (double)inputSize / MB_UNIT); fflush(NULL);
     }
     printf("\n");
 }
diff --git a/tests/bench/timefn.c b/tests/bench/timefn.c
index e3a05916..50e82722 100644
--- a/tests/bench/timefn.c
+++ b/tests/bench/timefn.c
@@ -137,8 +137,16 @@ PTime UTIL_getSpanTimeNano(UTIL_time_t begin, UTIL_time_t end)
 #else   /* relies on standard C90 (note : clock_t measurements can be wrong when using multi-threading) */
 
 UTIL_time_t UTIL_getTime(void) { return clock(); }
-PTime UTIL_getSpanTimeMicro(UTIL_time_t clockStart, UTIL_time_t clockEnd) { return 1000000ULL * (clockEnd - clockStart) / CLOCKS_PER_SEC; }
-PTime UTIL_getSpanTimeNano(UTIL_time_t clockStart, UTIL_time_t clockEnd) { return 1000000000ULL * (clockEnd - clockStart) / CLOCKS_PER_SEC; }
+
+PTime UTIL_getSpanTimeMicro(UTIL_time_t clockStart, UTIL_time_t clockEnd)
+{
+    return 1000000ULL * (PTime)(clockEnd - clockStart) / CLOCKS_PER_SEC;
+}
+
+PTime UTIL_getSpanTimeNano(UTIL_time_t clockStart, UTIL_time_t clockEnd)
+{
+    return 1000000000ULL * (PTime)(clockEnd - clockStart) / CLOCKS_PER_SEC;
+}
 
 #endif
 
diff --git a/tests/collisions/Makefile b/tests/collisions/Makefile
index 208090f9..abf4e8ce 100644
--- a/tests/collisions/Makefile
+++ b/tests/collisions/Makefile
@@ -26,9 +26,9 @@
 HEADER_DIRS = ./ ../../ allcodecs/
 CPPFLAGS += $(addprefix -I ,$(HEADER_DIRS))
 CFLAGS   += -Wall -Wextra -Wconversion \
-            -std=c11
+            -std=c11 $(MOREFLAGS)
 CXXFLAGS += -Wall -Wextra -Wconversion \
-            -std=c++11
+            -std=c++11 $(MOREFLAGS)
 LDFLAGS  += -pthread
 TESTHASHES = 3200000
 
diff --git a/tests/collisions/main.c b/tests/collisions/main.c
index 30aee4a4..c0c0cf84 100644
--- a/tests/collisions/main.c
+++ b/tests/collisions/main.c
@@ -687,7 +687,7 @@ static size_t search_collisions(
     int const hwidth = hashfnTable[hashID].bits;
     if (totalH == 0) totalH = select_nbh(hwidth);
     if (bflog == 0) bflog = highestBitSet(totalH) + 1;   /* auto-size filter */
-    uint64_t const bfsize = (1ULL << bflog);
+    assert(!filter || (0 <= bflog && bflog < 64));
 
 
     /* ===  filter hashes (optional)  === */
@@ -696,6 +696,7 @@ static size_t search_collisions(
     uint64_t maxNbH = totalH;
 
     if (filter) {
+        uint64_t const bfsize = 1ULL << bflog;
         time_t const filterTBegin = time(NULL);
         DISPLAY(" Creating filter (%i GB) \n", (int)(bfsize >> 30));
         bf = create_Filter(bflog);
diff --git a/tests/sanity_test.c b/tests/sanity_test.c
index e933cd4c..97146bb8 100644
--- a/tests/sanity_test.c
+++ b/tests/sanity_test.c
@@ -107,7 +107,8 @@ static void checkResult32(XXH32_hash_t r1, XXH32_hash_t r2, const char* testName
         return;
     }
 
-    XSUM_log("\rError: %s #%zd, line #%zd: Sanity check failed!\n", testName, testNb, lineNb);
+    XSUM_log("\rError: %s #%u, line #%u: Sanity check failed!\n",
+             testName, (unsigned)testNb, (unsigned)lineNb);
     XSUM_log("\rGot 0x%08X, expected 0x%08X.\n", (unsigned)r1, (unsigned)r2);
 
     if(abortByError) {
@@ -124,7 +125,8 @@ static void checkResult64(XXH64_hash_t r1, XXH64_hash_t r2, const char* testName
         return;
     }
 
-    XSUM_log("\rError: %s #%zd, line #%zd: Sanity check failed!\n", testName, testNb, lineNb);
+    XSUM_log("\rError: %s #%u, line #%u: Sanity check failed!\n",
+             testName, (unsigned)testNb, (unsigned)lineNb);
     XSUM_log("\rGot 0x%08X%08XULL, expected 0x%08X%08XULL.\n",
             (unsigned)(r1>>32), (unsigned)r1, (unsigned)(r2>>32), (unsigned)r2);
 
@@ -142,7 +144,8 @@ static void checkResult128(XXH128_hash_t r1, XXH128_hash_t r2, const char* testN
         return;
     }
 
-    XSUM_log("\rError: %s #%zd, line #%zd: Sanity check failed!\n", testName, testNb, lineNb);
+    XSUM_log("\rError: %s #%u, line #%u: Sanity check failed!\n",
+             testName, (unsigned)testNb, (unsigned)lineNb);
     XSUM_log("\rGot { 0x%08X%08XULL, 0x%08X%08XULL }, expected { 0x%08X%08XULL, 0x%08X%08XULL } \n",
             (unsigned)(r1.low64>>32), (unsigned)r1.low64, (unsigned)(r1.high64>>32), (unsigned)r1.high64,
             (unsigned)(r2.low64>>32), (unsigned)r2.low64, (unsigned)(r2.high64>>32), (unsigned)r2.high64 );
@@ -161,7 +164,8 @@ static void checkResultTestDataSample(const XSUM_U8* r1, const XSUM_U8* r2, cons
         return;
     }
 
-    XSUM_log("\rError: %s #%zd, line #%zd: Sanity check failed!\n", testName, testNb, lineNb);
+    XSUM_log("\rError: %s #%u, line #%u: Sanity check failed!\n",
+             testName, (unsigned)testNb, (unsigned)lineNb);
     XSUM_log("\rGot { 0x%02X, 0x%02X, 0x%02X, 0x%02X, 0x%02X }, expected { 0x%02X, 0x%02X, 0x%02X, 0x%02X, 0x%02X } \n",
             r1[0], r1[1], r1[2], r1[3], r1[4],
             r2[0], r2[1], r2[2], r2[3], r2[4] );
@@ -797,7 +801,7 @@ int main(int argc, const char* argv[])
 
     releaseSanityBuffer(sanityBuffer);
 
-    XSUM_log("\rOK. (passes %zd tests)\n", testCount);
+    XSUM_log("\rOK. (passes %u tests)\n", (unsigned)testCount);
 
     return EXIT_SUCCESS;
 }