diff --git a/src/common/cvt.cpp b/src/common/cvt.cpp
index f0c7f86e972..878538a69a4 100644
--- a/src/common/cvt.cpp
+++ b/src/common/cvt.cpp
@@ -1406,7 +1406,7 @@ double CVT_get_double(const dsc* desc, DecimalStatus decSt, ErrorFunction err, b
  *      Convert something arbitrary to a double precision number
  *
  **************************************/
-	double value;
+	double value = 0.0;
 
 	switch (desc->dsc_dtype)
 	{
diff --git a/src/common/unicode_util.cpp b/src/common/unicode_util.cpp
index 05ffe216b40..2101ecddc4a 100644
--- a/src/common/unicode_util.cpp
+++ b/src/common/unicode_util.cpp
@@ -1853,7 +1853,7 @@ USHORT UnicodeUtil::Utf16Collation::stringToKey(USHORT srcLen, const USHORT* src
 				if (keys)
 				{
 					UCHAR lastCharKey[BUFFER_TINY];	// sort key for a single character
-					ULONG prefixLen, lastCharKeyLen;
+					ULONG prefixLen = 0, lastCharKeyLen = 0;
 
 					srcLenLong -= i;
 
@@ -1877,8 +1877,6 @@ USHORT UnicodeUtil::Utf16Collation::stringToKey(USHORT srcLen, const USHORT* src
 						fb_assert(lastCharKey[lastCharKeyLen - 1] == '\0');
 						--lastCharKeyLen;
 					}
-					else
-						prefixLen = 0;
 
 					bool fallbackToPrefixKey = false;
 
diff --git a/src/gpre/pat.cpp b/src/gpre/pat.cpp
index 817ae409765..0a57f0ea2fc 100644
--- a/src/gpre/pat.cpp
+++ b/src/gpre/pat.cpp
@@ -179,9 +179,9 @@ void PATTERN_expand( USHORT column, const TEXT* pattern, PAT* args)
 	bool sw_gen = true;
 	p += align(p, column);
 
-	SSHORT value;				// value needs to be signed since some of the
-								// values printed out are signed.
-	SLONG long_value;
+	SSHORT value = 0;				// value needs to be signed since some of the
+	SLONG long_value = 0;			// values printed out are signed.
+
 	TEXT c;
 	while ((c = *pattern++))
 	{
diff --git a/src/jrd/btr.cpp b/src/jrd/btr.cpp
index bf010642fa1..f7cf9067b91 100644
--- a/src/jrd/btr.cpp
+++ b/src/jrd/btr.cpp
@@ -2315,15 +2315,13 @@ void BTR_reserve_slot(thread_db* tdbb, IndexCreation& creation)
 	}
 
 	UCHAR* desc = 0;
-	USHORT len, space;
+	const USHORT len = idx->idx_count * sizeof(irtd);
+	USHORT space = dbb->dbb_page_size;
 	index_root_page::irt_repeat* slot = NULL;
 	index_root_page::irt_repeat* end = NULL;
 
 	for (int retry = 0; retry < 2; ++retry)
 	{
-		len = idx->idx_count * sizeof(irtd);
-
-		space = dbb->dbb_page_size;
 		slot = NULL;
 
 		end = root->irt_rpt + root->irt_count;
@@ -2358,6 +2356,8 @@ void BTR_reserve_slot(thread_db* tdbb, IndexCreation& creation)
 		}
 		else
 			break;
+
+		space = dbb->dbb_page_size;
 	}
 
 	// If we didn't pick up an empty slot, allocate a new one
@@ -2816,8 +2816,8 @@ static void compress(thread_db* tdbb,
 	const Database* dbb = tdbb->getDatabase();
 	bool first_key = true;
 	VaryStr<MAX_KEY * 4> buffer;
-	size_t multiKeyLength;
-	UCHAR* ptr;
+	size_t multiKeyLength = 0;
+	UCHAR* ptr = nullptr;
 	UCHAR* p = key->key_data;
 	SSHORT scale = matchScale ? matchScale : desc->dsc_scale;
 
@@ -2829,7 +2829,7 @@ static void compress(thread_db* tdbb,
 
 		do
 		{
-			size_t length;
+			size_t length = 0;
 
 			has_next = false;
 
diff --git a/src/jrd/exe.cpp b/src/jrd/exe.cpp
index 3fbe78dc67c..4e972cc400c 100644
--- a/src/jrd/exe.cpp
+++ b/src/jrd/exe.cpp
@@ -555,7 +555,7 @@ void EXE_assignment(thread_db* tdbb, const ValueExprNode* to, dsc* from_desc, bo
 
 		if (null && to_desc->dsc_dtype <= dtype_varying)
 		{
-			USHORT minlen;
+			USHORT minlen = 0;
 
 			switch (to_desc->dsc_dtype)
 			{
diff --git a/src/jrd/filters.cpp b/src/jrd/filters.cpp
index 0d2e06e8504..fe0a1ae7f99 100644
--- a/src/jrd/filters.cpp
+++ b/src/jrd/filters.cpp
@@ -1044,22 +1044,14 @@ ISC_STATUS filter_transliterate_text(USHORT action, BlobControl* control)
 
 	// Do we already have enough bytes in temp buffer to fill output buffer?
 
-	bool can_use_more;
+	bool can_use_more = true;
 	USHORT length = aux->ctlaux_buffer1_unused;
-	if (length)
+	// Always keep a minimal count of bytes in the input buffer
+	// to prevent the case of truncated characters.
+	if (length >= 4 && control->ctl_buffer_length < (length * aux->ctlaux_expansion_factor / EXP_SCALE))
 	{
-		if (control->ctl_buffer_length < (length * aux->ctlaux_expansion_factor / EXP_SCALE))
-		{
-			// No need to fetch more bytes, we have enough pending
-			can_use_more = false;
-		}
-		else
-			can_use_more = true;
-
-		// Always keep a minimal count of bytes in the input buffer,
-		// to prevent the case of truncated characters.
-		if (length < 4)
-			can_use_more = true;
+		// No need to fetch more bytes, we have enough pending
+		can_use_more = false;
 	}
 
 	/* Load data into the temporary buffer if,
@@ -1071,8 +1063,7 @@ ISC_STATUS filter_transliterate_text(USHORT action, BlobControl* control)
 
 	USHORT bytes_read_from_source = 0;
 
-	///if (!length || (can_use_more && (aux->ctlaux_source_blob_status == isc_segment)))
-	if (!length || can_use_more)
+	if (can_use_more)
 	{
 		// Get a segment, or partial segment, from the source
 		// into the temporary buffer
diff --git a/src/jrd/recsrc/FilteredStream.cpp b/src/jrd/recsrc/FilteredStream.cpp
index 744ebf484dd..be7ce534793 100644
--- a/src/jrd/recsrc/FilteredStream.cpp
+++ b/src/jrd/recsrc/FilteredStream.cpp
@@ -187,7 +187,7 @@ bool FilteredStream::evaluateBoolean(thread_db* tdbb) const
 	// on the right.
 
 	// ANY/ALL select node pointer
-	const BoolExprNode* select_node;
+	const BoolExprNode* select_node = nullptr;
 
 	// ANY/ALL column node pointer
 	const BoolExprNode* column_node = m_anyBoolean;
@@ -203,8 +203,6 @@ bool FilteredStream::evaluateBoolean(thread_db* tdbb) const
 			select_node = booleanNode->arg1;
 			column_node = booleanNode->arg2;
 		}
-		else
-			select_node = NULL;
 	}
 
 	if (column_node && m_ansiAny)
diff --git a/src/utilities/guard/guard.cpp b/src/utilities/guard/guard.cpp
index fbd96db318f..e32bebd1963 100644
--- a/src/utilities/guard/guard.cpp
+++ b/src/utilities/guard/guard.cpp
@@ -183,7 +183,6 @@ int CLIB_ROUTINE main( int argc, char **argv)
 	time_t timer = 0;
 
 	do {
-		int ret_code;
 
 		if (shutting_down)
 		{
@@ -226,6 +225,7 @@ int CLIB_ROUTINE main( int argc, char **argv)
 		}
 
 		// wait for child to die, and evaluate exit status
+		int ret_code = NORMAL_EXIT;
 		bool shutdown_child = true;
 		if (!shutting_down)
 		{
diff --git a/src/yvalve/gds.cpp b/src/yvalve/gds.cpp
index ce575729601..96b8a470081 100644
--- a/src/yvalve/gds.cpp
+++ b/src/yvalve/gds.cpp
@@ -3173,7 +3173,7 @@ static int blr_print_dtype(gds_ctl* control)
  *	data described.
  *
  **************************************/
-	SSHORT length;
+	SSHORT length = 0;
 
 	const USHORT dtype = control->ctl_blr_reader.getByte();
 
@@ -3537,7 +3537,7 @@ static void blr_print_verb(gds_ctl* control, SSHORT level)
 	blr_print_blr(control, blr_operator);
 	level++;
 	const UCHAR* ops = blr_print_table[blr_operator].blr_operators;
-	SSHORT n;
+	SSHORT n = 0;
 
 	while (*ops)
 	{