diff --git a/doc/sql.extensions/README.floating_point_types.md b/doc/sql.extensions/README.floating_point_types.md
new file mode 100644
index 0000000000..ecc06efa46
--- /dev/null
+++ b/doc/sql.extensions/README.floating_point_types.md
@@ -0,0 +1,55 @@
+# Floating point types
+
+Firebird has two forms of floating point types:
+
+- approximate numeric types (or binary floating point types)
+- decimal floating point types
+
+## Approximate numeric types
+
+The approximate numeric types supported by Firebird are a 32 bit single 
+precision and a 64 bit double precision floating point type. These types are
+available with the following SQL standard type names:
+
+- `REAL` - 32 bit single precision (synonym for `FLOAT`) _(1)_
+- `FLOAT` - 32 bit single precision
+- `FLOAT(p)` where `p` is the precision of the significand in binary digits _(2, 3)_
+	- 1 <= `p` <= 24 - 32 bit single precision (synonym for `FLOAT`)
+	- 25 <= `p` <= 53 - 64 bit double precision (synonym for `DOUBLE PRECISION`)
+- `DOUBLE PRECISION` - 64 bit double precision
+
+In addition the following non-standard type names are supported:
+
+- `LONG FLOAT` - 64 bit double precision (synonym for `DOUBLE PRECISION`)
+- `LONG FLOAT(p)` where `p` is the precision of the significand in binary digits _(4, 5)_
+	- 1 <= `p` <= 53 - 64 bit double precision (synonym for `DOUBLE PRECISION`)
+
+These non-standard type names are deprecated and they may be removed in a future 
+version.
+
+## Decimal floating point types
+
+The decimal floating point types supported by Firebird are a 64 bit Decimal64
+with a precision of 16 decimals and a 128 bit Decimal128 with a precision of
+34 decimals. These types are available with the following SQL standard type 
+names:
+
+- `DECFLOAT` - 128 bit Decimal128 (synonym for `DECFLOAT(34)`)
+- `DECFLOAT(16)` - 64 bit Decimal64
+- `DECFLOAT(34)` - 128 bit Decimal128
+
+## Notes
+
+1. `REAL` has been available as a synonym for `FLOAT` since Firebird 1 and even 
+earlier, but was never documented.
+2. Firebird 3 and earlier supported `FLOAT(p)` where `p` was the 
+approximate precision in decimal digits, and 0 <= `p` <= 7 mapped to 32 bit 
+single precision and `p` > 7 to 64 bit double precision. This syntax was never 
+documented.
+3. For `p` in `FLOAT(p)`, the values 1 <= `p` <= 24 are all treated as 
+`p` = 24, values 25 <= `p` <= 53 are all handled as `p` = 53.
+4. Firebird 3 and earlier supported `LONG FLOAT(p)` where `p` was the 
+approximate precision in decimal digits, where any value for `p` mapped to 
+64 bit double precision. This type name and syntax were never documented.
+3. For `p` in `LONG FLOAT(p)`, the values 1 <= `p` <= 53 are all handled as 
+`p` = 53.
diff --git a/src/dsql/parse.y b/src/dsql/parse.y
index 5b2a82588c..7362a43b53 100644
--- a/src/dsql/parse.y
+++ b/src/dsql/parse.y
@@ -5095,11 +5095,19 @@ decimal_keyword
 
 %type <legacyField> float_type
 float_type
-	: FLOAT precision_opt
+	: FLOAT precision_opt_nz
 		{
+		    // Precision is binary digits of the significand: 1-24 for 32 bit single precision, 25-53 for 64 bit double precision
+			// Precision 0 is the 'no precision specified' case, which defaults to 32 bit single precision
+			SLONG precision = $2;
+
+			if (precision != 0 && (precision < 1 || precision > 53))
+				yyabandon(YYPOSNARG(2), -842, Arg::Gds(isc_precision_err2) << Arg::Num(1) << Arg::Num(53));
+																// Precision must be between 1 and 53
+
 			$$ = newNode<dsql_fld>();
 
-			if ($2 > 7)
+			if (precision > 24)
 			{
 				$$->dtype = dtype_double;
 				$$->length = sizeof(double);
@@ -5110,8 +5118,16 @@ float_type
 				$$->length = sizeof(float);
 			}
 		}
-	| LONG FLOAT precision_opt
+	| LONG FLOAT precision_opt_nz
 		{
+			// Precision is binary digits of the significand: 1-53 for 64 bit double precision
+			// Precision 0 is the 'no precision specified case', which defaults to 64 bit double precision
+			SLONG precision = $3;
+
+			if (precision != 0 && (precision < 1 || precision > 53))
+				yyabandon(YYPOSNARG(3), -842, Arg::Gds(isc_precision_err2) << Arg::Num(1) << Arg::Num(53));
+																// Precision must be between 1 and 53
+
 			$$ = newNode<dsql_fld>();
 			$$->dtype = dtype_double;
 			$$->length = sizeof(double);
@@ -5130,13 +5146,7 @@ float_type
 		}
 	;
 
-%type <int32Val> precision_opt
-precision_opt
-	: /* nothing */					{ $$ = 0; }
-	| '(' nonneg_short_integer ')'	{ $$ = $2; }
-	;
-
-// alternative to precision_opt that does not allow zero
+// optional precision that does not allow zero
 %type <int32Val> precision_opt_nz
 precision_opt_nz
 	: /* nothing */				{ $$ = 0; }