diff --git a/locale.c b/locale.c
index 4992f5e937ad..5773f9ebd48c 100644
--- a/locale.c
+++ b/locale.c
@@ -1474,7 +1474,9 @@ S_parse_LC_ALL_string(pTHX_ const char * string,
         }
     }
 
-    const char * msg;
+    /* Some compilers don't realize all paths initialize this */
+    const char * msg = NULL;
+
     const char * display_start = s;
     const char * display_end = e;
 
diff --git a/mg.c b/mg.c
index 4dad61f3e41c..08c8e23ebd32 100644
--- a/mg.c
+++ b/mg.c
@@ -3803,6 +3803,7 @@ Perl_perly_sighandler(int sig, Siginfo_t *sip PERL_UNUSED_DECL,
             /* Not clear if this will work */
             /* XXX not clear if this should be protected by 'if (safe)'
              * too */
+            PERL_UNUSED_ARG(safe);
 
             (void)rsignal(sig, SIG_IGN);
             (void)rsignal(sig, PL_csighandlerp);
diff --git a/perl.c b/perl.c
index 12117d04e5f1..1881ffc51739 100644
--- a/perl.c
+++ b/perl.c
@@ -4406,7 +4406,9 @@ S_init_ids(pTHX)
 bool
 Perl_doing_taint(int argc, char *argv[], char *envp[])
 {
-#ifndef PERL_IMPLICIT_SYS
+#ifdef PERL_IMPLICIT_SYS
+    PERL_UNUSED_ARG(envp);
+#else
     /* If we have PERL_IMPLICIT_SYS we can't call getuid() et alia
      * before we have an interpreter-- and the whole point of this
      * function is to be called at such an early stage.  If you are on
diff --git a/pp_hot.c b/pp_hot.c
index e95553463f7d..89e0c8cbf9e2 100644
--- a/pp_hot.c
+++ b/pp_hot.c
@@ -359,7 +359,7 @@ PP(pp_aelemfastlex_store)
 
     /* inlined av_fetch() for simple cases ... */
     if (!SvRMAGICAL(av) && key >=0 && key <= AvFILLp(av)) {
-        targ = AvARRAY(av)[key];
+        targ = AvARRAY(av)[ (U8) key ];
     }
     /* ... else do it the hard way */
     if (!targ) {
@@ -1590,7 +1590,7 @@ PP(pp_readline)
         SvGETMAGIC(arg);
 
         /* unrolled tryAMAGICunTARGETlist(iter_amg, 0) */
-        SV *tmpsv;
+        SV *tmpsv = NULL;
         U8 gimme = GIMME_V;
         if (UNLIKELY(SvAMAGIC(arg) &&
             (tmpsv = amagic_call(arg, &PL_sv_undef, iter_amg,
@@ -2033,7 +2033,7 @@ PP(pp_aelemfast)
 
     /* inlined av_fetch() for simple cases ... */
     if (!SvRMAGICAL(av) && key >= 0 && key <= AvFILLp(av)) {
-        sv = AvARRAY(av)[key];
+        sv = AvARRAY(av)[ (U8) key ];
         if (sv)
             goto ret;
         if (!lval) {
diff --git a/pp_sys.c b/pp_sys.c
index 9a47afd82bc3..4e542c6c1ca7 100644
--- a/pp_sys.c
+++ b/pp_sys.c
@@ -392,7 +392,7 @@ PP(pp_glob)
 
     /* unrolled
       tryAMAGICunTARGETlist(iter_amg, (PL_op->op_flags & OPf_SPECIAL)); */
-    SV *tmpsv;
+    SV *tmpsv = NULL;
     U8 gimme = GIMME_V;
     if (UNLIKELY(SvAMAGIC(arg) &&
         (tmpsv = amagic_call(arg, &PL_sv_undef, iter_amg,
@@ -5558,6 +5558,7 @@ PP_wrapped(pp_shostent, 1, 0)
 {
     dSP;
     const int stayopen = TOPi;
+    PERL_UNUSED_VAR(stayopen);
     switch(PL_op->op_type) {
     case OP_SHOSTENT:
 #ifdef HAS_SETHOSTENT
diff --git a/toke.c b/toke.c
index ece6bb56d5e5..af34fd672211 100644
--- a/toke.c
+++ b/toke.c
@@ -12458,7 +12458,7 @@ Perl_scan_num(pTHX_ const char *start, YYSTYPE* lvalp)
     const char *lastub = NULL;		/* position of last underbar */
     static const char* const number_too_long = "Number too long";
     bool warned_about_underscore = 0;
-    I32 shift; /* shift per digit for hex/oct/bin, hoisted here for fp */
+    I32 shift = 0; /* shift per digit for hex/oct/bin, hoisted here for fp */
 #define WARN_ABOUT_UNDERSCORE() \
         do { \
             if (!warned_about_underscore) { \
diff --git a/util.c b/util.c
index eddba602d12a..7d037f65ee11 100644
--- a/util.c
+++ b/util.c
@@ -2940,6 +2940,7 @@ Perl_rsignal(pTHX_ int signo, Sighandler_t handler)
 static Signal_t
 sig_trap(int signo)
 {
+    PERL_UNUSED_ARG(signo);
     PL_sig_trapped++;
 }
 
diff --git a/win32/fcrypt.c b/win32/fcrypt.c
index f2836eddd250..88a23f341d11 100644
--- a/win32/fcrypt.c
+++ b/win32/fcrypt.c
@@ -2,6 +2,8 @@
 /* Copyright (C) 1993 Eric Young - see README for more details */
 #include <stdio.h>
 #include <errno.h>
+#include "EXTERN.h"
+#include "perl.h"
 
 /* Eric Young.
  * This version of crypt has been developed from my MIT compatible
@@ -466,12 +468,10 @@ unsigned const char cov_2char[64]={
 };
 
 /* the salt for classic DES crypt (which is all we implement here)
-   permits [./0-9A-Za-z], since '.' and '/' immediately precede
-   '0' we don't need individual checks for '.' and '/' 
+   permits [./0-9A-Za-z], since '.' and '/' are adjacent, we don't need
+   individual checks for them
 */
-#define good_for_salt(c) \
-    ((c) >= '.' && (c) <= '9' || (c) >= 'A' && (c) <= 'Z' ||  \
-     (c) >= 'a' && (c) <= 'z')
+#define good_for_salt(c) (isALPHANUMERIC(c) || inRANGE((c), '.', '/'))
 
 char *
 des_fcrypt(const char *buf, const char *salt, char *buff)
diff --git a/win32/perllib.c b/win32/perllib.c
index efae2d817b8d..15cef6ebb731 100644
--- a/win32/perllib.c
+++ b/win32/perllib.c
@@ -261,7 +261,7 @@ EXTERN_C		/* GCC in C++ mode mangles the name, otherwise */
 BOOL APIENTRY
 DllMain(HINSTANCE hModule,	/* DLL module handle */
         DWORD fdwReason,	/* reason called */
-        LPVOID lpvReserved)	/* reserved */
+        LPVOID)                 /* reserved */
 { 
     switch (fdwReason) {
         /* The DLL is attaching to a process due to process
diff --git a/win32/vmem.h b/win32/vmem.h
index 3d5492958756..e59096d9bf21 100644
--- a/win32/vmem.h
+++ b/win32/vmem.h
@@ -61,28 +61,33 @@ inline void MEMODSlx(char *str, long x)
    Even though perl links with ucrtbase.dll, there is alot of overhead for
    using ::new() operator. Just implement our own ::new(), more C-style. */
 #define VMEM_H_NEW_OP \
-    void* operator new(size_t size) noexcept {  \
-      void * p = (void*)win32_malloc(size); \
-      if(!p) noperl_die("%s%s","Out of memory in perl:", "???"); return p; }; \
-    void* operator new[](size_t size) noexcept { \
-      void * p = (void*)win32_malloc(size); \
-      if(!p) noperl_die("%s%s","Out of memory in perl:", "???"); return p; }; \
-    void* operator new( size_t size, int block_use, \
-                          char const* file_name, int line_number) noexcept { \
-        UNREFERENCED_PARAMETER(block_use); \
-        UNREFERENCED_PARAMETER(file_name); \
-        UNREFERENCED_PARAMETER(line_number); \
-        void * p = (void*)win32_malloc(size); \
-        if(!p) noperl_die("%s%s","Out of memory in perl:", "???"); return p; \
-    }; \
-    void* operator new[]( size_t size, int block_use, \
-                          char const* file_name, int line_number) noexcept { \
-        UNREFERENCED_PARAMETER(block_use); \
-        UNREFERENCED_PARAMETER(file_name); \
-        UNREFERENCED_PARAMETER(line_number); \
-         void * p = (void*)win32_malloc(size); \
-         if(!p) noperl_die("%s%s","Out of memory in perl:", "???"); return p; }; \
-    void operator delete (void* p) noexcept { win32_free(p); return; }; \
+    void* operator new(size_t size) noexcept {                              \
+        void * p = (void*)win32_malloc(size);                               \
+        if (!p) noperl_die("%s%s","Out of memory in perl:", "???");         \
+        return p;                                                           \
+    };                                                                      \
+    void* operator new[](size_t size) noexcept {                            \
+        void * p = (void*)win32_malloc(size);                               \
+        if (!p) noperl_die("%s%s","Out of memory in perl:", "???");         \
+        return p; };                                                        \
+    void* operator new( size_t size, int block_use,                         \
+                          char const* file_name, int line_number) noexcept {\
+        UNREFERENCED_PARAMETER(block_use);                                  \
+        UNREFERENCED_PARAMETER(file_name);                                  \
+        UNREFERENCED_PARAMETER(line_number);                                \
+        void * p = (void*)win32_malloc(size);                               \
+        if(!p) noperl_die("%s%s","Out of memory in perl:", "???");          \
+        return p;                                                           \
+    };                                                                      \
+    void* operator new[]( size_t size, int block_use,                       \
+                          char const* file_name, int line_number) noexcept {\
+        UNREFERENCED_PARAMETER(block_use);                                  \
+        UNREFERENCED_PARAMETER(file_name);                                  \
+        UNREFERENCED_PARAMETER(line_number);                                \
+        void * p = (void*)win32_malloc(size);                               \
+        if(!p) noperl_die("%s%s","Out of memory in perl:", "???");          \
+        return p; };                                                        \
+    void operator delete (void* p) noexcept { win32_free(p); return; };     \
     void operator delete[] (void* p) noexcept { win32_free(p);  return; }
 
 
@@ -210,7 +215,7 @@ VMem::VMem(void)
 {
 #ifdef _USE_LINKED_LIST
     InitializeCriticalSection(&m_cs);
-#endif _USE_LINKED_LIST
+#endif /* _USE_LINKED_LIST */
     m_lRefCount =  1;
     return;
 }
diff --git a/win32/win32.h b/win32/win32.h
index 1b69d153c1f7..cd12a2fe3721 100644
--- a/win32/win32.h
+++ b/win32/win32.h
@@ -133,7 +133,8 @@
 #    define NOMEMMGR          /* GUI IPC RPC malloc buffers */
 #    define NOMENUS           /* GUI Menu obj */
 #    define NOMETAFILE        /* file format for half rendered graphics */
-#    define NOMINMAX          /* "Macros min(a,b) and max(a,b)" OBSOL/UNIMPL/FUT */
+#    undef NOMINMAX           /* "Macros min(a,b) and max(a,b)" OBSOL/UNIMPL/FUT */
+#    define NOMINMAX
 #    define NOMSG             /* GUI Message loop */
 /* #define NONLS              "Wide" Code Page conversion APIs */
 /* OBSOL/UNIMPL/FUT "OpenFile(), OemToAnsi, AnsiToOem" etc */
diff --git a/win32/win32sck.c b/win32/win32sck.c
index 7289a47d9b0b..6bfdee4f9e86 100644
--- a/win32/win32sck.c
+++ b/win32/win32sck.c
@@ -780,6 +780,7 @@ win32_getnetent(void)
 struct netent *
 win32_getnetbyname(char *name) 
 {
+    PERL_UNUSED_ARG(name);
     win32_croak_not_implemented("getnetbyname");
     return (struct netent *)NULL;
 }
@@ -787,6 +788,8 @@ win32_getnetbyname(char *name)
 struct netent *
 win32_getnetbyaddr(long net, int type) 
 {
+    PERL_UNUSED_ARG(net);
+    PERL_UNUSED_ARG(type);
     win32_croak_not_implemented("getnetbyaddr");
     return (struct netent *)NULL;
 }
@@ -808,6 +811,7 @@ win32_getservent(void)
 void
 win32_sethostent(int stayopen)
 {
+    PERL_UNUSED_ARG(stayopen);
     win32_croak_not_implemented("sethostent");
 }
 
@@ -815,6 +819,7 @@ win32_sethostent(int stayopen)
 void
 win32_setnetent(int stayopen)
 {
+    PERL_UNUSED_ARG(stayopen);
     win32_croak_not_implemented("setnetent");
 }
 
@@ -822,6 +827,7 @@ win32_setnetent(int stayopen)
 void
 win32_setprotoent(int stayopen)
 {
+    PERL_UNUSED_ARG(stayopen);
     win32_croak_not_implemented("setprotoent");
 }
 
@@ -829,6 +835,7 @@ win32_setprotoent(int stayopen)
 void
 win32_setservent(int stayopen)
 {
+    PERL_UNUSED_ARG(stayopen);
     win32_croak_not_implemented("setservent");
 }