diff --git a/lib/comp.c b/lib/comp.c
index 6c4f56e..1d5b8fd 100644
--- a/lib/comp.c
+++ b/lib/comp.c
@@ -4305,7 +4305,9 @@ static int compile_cons_xlist_expression (hcl_t* hcl, hcl_cnode_t* obj, int nret
 	}
 	else
 	{
-		hcl_setsynerrbfmt (hcl, HCL_SYNERR_CALLABLE, HCL_CNODE_GET_LOC(car), HCL_CNODE_GET_TOK(car), "invalid callable in function call");
+		hcl_setsynerrbfmt (hcl, HCL_SYNERR_CALLABLE, HCL_CNODE_GET_LOC(car), HCL_NULL,
+			"invalid callable '%.*js' in function call",
+			HCL_CNODE_GET_TOKLEN(car), HCL_CNODE_GET_TOKPTR(car));
 		return -1;
 	}
 
@@ -4679,9 +4681,8 @@ HCL_UNUSED static int string_to_ooi (hcl_t* hcl, hcl_oocs_t* str, int radixed, h
 
 		if (base < 2 || base > 36)
 		{
-		invalid_radix_value:
 			hcl_seterrbfmt (hcl, HCL_EINVAL,
-				"invalid radix value '%d' in radixed number '%.*js'", base, str->len, str->ptr);
+				"unsupported radix '%d' in radixed number '%.*js'", base, str->len, str->ptr);
 			return -1;
 		}
 	}
@@ -4731,7 +4732,10 @@ static hcl_oop_t string_to_num (hcl_t* hcl, hcl_oocs_t* str, const hcl_loc_t* lo
 	end = str->ptr + str->len;
 
 	/* [NOTE]
-	 *   The code here assumes that the reader ensures that
+	 * - this is not a generic conversion functionu
+	 * - it assumes a certain pre-sanity check on the string
+	 *   done by the lexical analyzer.
+	 * - it also assumes that the reader ensures that
 	 *   there is at least 1 valid digit after radix specifier. */
 
 	HCL_ASSERT (hcl, ptr < end);
@@ -4774,13 +4778,14 @@ static hcl_oop_t string_to_num (hcl_t* hcl, hcl_oocs_t* str, const hcl_loc_t* lo
 			ptr++;
 		}
 
+		HCL_ASSERT (hcl, base >= 2 && base <= 36); /* the lexer must guarantee this */
+		/*
 		if (base < 2 || base > 36)
 		{
-		invalid_radix_value:
 			hcl_setsynerrbfmt (hcl, HCL_SYNERR_RADIX, loc, HCL_NULL,
-				"invalid radix value '%d' in radixed number '%.*js'", base, str->len, str->ptr);
+				"unsupported radix '%d' in radixed number '%.*js'", base, str->len, str->ptr);
 			return HCL_NULL;
-		}
+		}*/
 	}
 
 /* TODO: handle floating point numbers ... etc */
diff --git a/lib/read.c b/lib/read.c
index 1173b32..ecd5052 100644
--- a/lib/read.c
+++ b/lib/read.c
@@ -3124,10 +3124,10 @@ static int flx_plain_number (hcl_t* hcl, hcl_ooci_t c) /* number */
 		if (!pn->fpdec && pn->tok_type == HCL_TOK_NUMLIT && pn->digit_count[0] > 0 && c == 'r')
 		{
 			/* 16rABCD */
-			if (pn->radix_cand_overflown)
+			if (pn->radix_cand_overflown || pn->radix_cand < 2 || pn->radix_cand > 36)
 			{
 				hcl_setsynerrbfmt (hcl, HCL_SYNERR_NUMLIT, TOKEN_LOC(hcl), HCL_NULL,
-					"radix too large '%.*js' before '%jc'",
+					"unsupported radix '%.*js' before '%jc'",
 					TOKEN_NAME_LEN(hcl), TOKEN_NAME_PTR(hcl), c);
 				return -1;
 			}
diff --git a/t/feed-5001.err b/t/feed-5001.err
index 0037698..fad872e 100644
--- a/t/feed-5001.err
+++ b/t/feed-5001.err
@@ -111,7 +111,22 @@ printf "%O\n"  35rabcdefghijklzabcd ##ERROR: syntax error - invalid numeric lite
 
 ---
 
-+ 12389127398127389217382197283197321897r11221 1 ##ERROR: syntax error - radix too large '12389127398127389217382197283197321897' before 'r'
++ 12389127398127389217382197283197321897r11221 1 ##ERROR: syntax error - unsupported radix '12389127398127389217382197283197321897' before 'r'
+
+---
+
++ 0000r11221 1 ##ERROR: syntax error - unsupported radix '0000' before 'r'
+---
+
++ 0r11221 1 ##ERROR: syntax error - unsupported radix '0' before 'r'
+
+---
+
++ 1r11221 1 ##ERROR: syntax error - unsupported radix '1' before 'r'
+
+---
+
++ 37r11221 1 ##ERROR: syntax error - unsupported radix '37' before 'r'
 
 ---